The Australian Meat Processor Corporation acknowledges the matching funds provided by the Australian Government to support the research and development detailed in this publication.

PROJECT CODE: 2017-1038

PREPARED BY: Roberta Fornarelli, Parisa A. Bahri, Navid Moheimani

DATE SUBMITTED: 2-October-2017

DATE PUBLISHED: 29-November-2017

PUBLISHED BY: AMPC

Utilization of microalgae to purify waste streams and production of value added products

TABLE OF CONTENTS

TABLE OF CONTENTS .................................................................................................................. 2

GLOSSARY ................................................................................................................................... 4

1.0 EXECUTIVE SUMMARY ................................................................................................... 5

2.0 INTRODUCTION .............................................................................................................. 7

3.0 PROJECT OBJECTIVES ..................................................................................................... 8

4.0 METHODOLOGY ........................................................................................................... 10

4.1 Literature review and data collection .............................................................. 10

4.2 Mass balance of the microalgae cultivation system ........................................ 11

4.3 Energy balance of the microalgae cultivation system ..................................... 13

4.4 Environmental impact assessment .................................................................. 14

4.5 Cost-benefit analysis of the microalgae cultivation system ............................ 15

4.6 Sensitivity and uncertainty analysis ................................................................. 16

5.0 PROJECT OUTCOMES ................................................................................................... 18

5.1 Milestone 1. Literature review and data collection ......................................... 18

5.1.1 The red meat processing industry and its environmental impacts ..... 18

5.1.2 Wastewater characterization and treatment ...................................... 20

5.1.3 Food safety standards applicable to the meat processing industry .... 24

5.2 Milestone 2. An integrated microalgae cultivation system for the red meat processing industry ...................................................................................................... 26

5.3 Milestone 3. Alternative water sources identification and wastewater quality assessment ................................................................................................................... 27

5.4 Milestone 4. Algae-cultivation system design ................................................. 29

5.4.1 Microalgae cultivation approach ......................................................... 29

5.4.2 Mass and energy balances at selected abattoirs ................................. 31

5.4.3 Mass and energy balances of the anaerobic digestion of algae biomass 35

5.5 Milestone 5. Environmental impact analysis ................................................... 40

5.6 Milestone 6. Cost benefit and uncertainty analysis ........................................ 41

5.6.1 Cost benefit analysis of the proposed microalgae cultivation system 41

5.6.2 Sensitivity and uncertainty analysis ..................................................... 44

6.0 DISCUSSION .................................................................................................................. 49

7.0 CONCLUSIONS/RECOMMENDATIONS ......................................................................... 54

8.0 BIBLIOGRAPHY ............................................................................................................. 55

9.0 APPENDICES ................................................................................................................. 62

9.1 Appendix 1. Reviewed Australian abattoirs ..................................................... 62

9.1.1 Processing Site A .................................................................................. 62

9.1.2 Processing Site B .................................................................................. 64

9.1.3 Processing Site C .................................................................................. 65

9.1.4 Processing Site D .................................................................................. 67

9.1.5 Processing Site E .................................................................................. 68

9.1.6 Processing Site F................................................................................... 70

9.1.7 Processing Site G .................................................................................. 72

9.2 Appendix 2. Review of microalgae cultivation systems ................................... 81

9.2.1 Microalgae cultivation systems ........................................................... 81

9.2.2 Current applications of microalgae cultivation systems in wastewater treatment ......................................................................................................... 83

9.2.3 Application of microalgae cultivation in the meat processing industry 85

9.3 Appendix 3. Alternative water sources for integration with microalgae cultivation .................................................................................................................... 89

9.3.1 Site G abattoir ...................................................................................... 89

9.3.2 Site A, C and D abattoirs ...................................................................... 91

9.4 Appendix 4. Environmental impact and risk assessment ................................ 99

9.4.1 Guidelines for recycling of wastewater effluents in abattoirs ............ 99

9.4.2 Conventional treatment process at Sites A, D and G .......................... 99

9.4.3 Microalgae cultivation system at Sites D and G ................................ 103

9.4.4 Review of LCA studies on microalgae cultivation .............................. 107

9.4.5 Final use of the algae biomass and its environmental impact .......... 110

GLOSSARY AMPC: Australian Meat Processor Corporation

AGWR: Australian Guidelines for Water Recycling

AD: Anaerobic Digestion

BOD: Biological Oxygen Demand

COD: Chemical Oxygen Demand

CO2: carbon dioxide

FOG: Fat, Oil and Grease

HRT: Hydraulic Retention Time

HSCW: Hot Standard Carcass Weight

MLA: Meat and Livestock Australia

NH4-N: Ammonium as nitrogen

NO2-N: Nitrite as nitrogen

NO3-N: Nitrate as nitrogen

PO4-P: Phosphate as phosphorus

SCOD: Soluble COD

TCOD: Total COD

TDS: Total Dissolved Solids

Temp: Temperature

TKN: Total Kjeldahl Nitrogen

TKP: Total Kjeldahl Phosphorus

TN: Total Nitrogen

TOC: Total Organic Carbon

TP: Total Phosphorus

TS: Total Solids

TSS: Total Suspended Solids

VS: Volatile Solids

1.0 EXECUTIVE SUMMARY As a substantial consumer of water, the Australian red meat processing industry produces large

volumes of wastewater that are rich in nutrients and organic matter. On-site treatment of

wastewater is needed to ensure compliance with the existing guidelines for safe discharge and

recycle. The majority of Australian abattoirs have wastewater treatment plants on-site, most of

which includes anaerobic digestion (AD) as the main biological treatment aiming at reducing the

organic content. High concentrations of nitrogen and phosphorous are found in the AD effluents and

nutrient removal treatments are not as widely implemented as anaerobic treatments. As a

consequence, large volumes of high nutrient content wastewater are dumped in evaporation ponds.

Environmental risks of such management practice are associated with greenhouse gas emissions by

ammonia volatilization, eutrophication of soils and surface waters due to nutrient imbalance, and

groundwater nitrogen contamination. Large land footprint and loss of the environmental and

economic value of the wastewater effluent in the form of water and nutrients recovery are major

drawbacks of the current management practices. Due to the environmental and economic burden

caused by the current wastewater treatment practice, a cost effective and efficient nutrient

removal/recovery system is perceived a priority by the red meat processing industry. Waste-to-profit

recovery systems that allow the recycle of treated wastewater as well as the production of value

added products are considered as a major progress within the industry towards environmental

sustainability, economic benefit and process optimization.

Overarching objective of this project is to investigate a new technological approach for the

transformation of nutrient contents in red meat processing wastewater streams into protein rich

biomass via microalgae cultivation. To address this main objective, a techno-economic feasibility

study of an integrated microalgae cultivation process for treating abattoir wastewater effluents and

for water recycling has been developed. A thorough literature review has demonstrated the maturity

and robustness of microalgae cultivation as a cost-effective treatment technology able to capture

nutrient and harvest algae biomass whilst producing a nutrient-depleted water effluent. Through the

development of a mathematical model, the output of a microalgae cultivation system integrated on

the AD effluents currently generated at two Australian abattoirs has been quantified. The treatment

of alternative wastewater streams by microalgae cultivation has been addressed and the effluent

from AD was demonstrated as the most suitable stream for integration with the proposed process.

As part of the project objectives, the potential for the effluent from microalgae cultivation to be

reused and recycled within the abattoir’s operations has been addressed through an environmental

and risk assessment in the light of current Australian food safety standards.

The proposed microalgae cultivation system generates two product streams: i) a concentrated

microalgae biomass product and ii) a nutrient-depleted water effluent. A microalgae cultivation

system that receives 2 ML/d of AD effluent is expected to generate about 1.3 ML/d of nutrient-

depleted water suitable for recycle/discharge and about 3 to 5 tons of algae biomass product at 30%

solids. At an average concentration of nitrogen and phosphorous in the AD effluent ranging as 150-

250 mg/L and 25-35 mg/L, respectively, an 80% to 100% nutrient removal and fixation of 6 to 10

tons/d of carbon dioxide into algae biomass are foreseen. Capital and operational costs are

estimated at AUD 2-4M and AUD 1-2M, respectively, for an open raceway pond algae cultivation

system followed by settling and centrifugation. Algae unit production costs range within AUD 1.5 to 2

per kg of algae product, thus competitive with the current market price of microalgae sold as animal

feed (ranging from AUD 5 to 20 per kg of algae) or fish meal (ranging from AUD 1.5 to 2.15 per kg of

algae).

Subjected to water recycling guidelines implemented at each abattoir, the nutrient-depleted water

stream can be recycled within the abattoir operations thus improving the environmental impact of

the abattoir and reducing costs associated with purchase of freshwater. Suggested uses of the

effluent from microalgae cultivation refer to all the processes where non-potable quality water is

allowed for use, e.g., cleaning of yards, infrastructures and trucks, washing of animals other than

final wash, animal drinking water, fire control, irrigation of gardens and green areas, irrigation of

crops and pasture for fodder production. If recycle is not viable, the final effluent is likely to meet the

guidelines for safe discharge into the sewer or surface waters. The grown algae biomass represents a

process by-product whose intrinsic value can be exploited as a way to offset some treatment costs

and possibly produce a revenue stream. On-site use of algae biomass as fertilizer and animal feed are

technically feasible and cost effective options. Algae biomass can also be used for producing biogas

through AD, thus offsetting some of the abattoir energy demand.

The integrated microalgae cultivation system mitigates, and possibly removes, the environmental

impacts associated with contamination of soils, water and groundwater, and with greenhouse gas

emissions into the air. More importantly, it gives value to the wastewater effluent by recovering the

nutrients and water and ultimately improving the environmental footprint of the abattoir. Several

positive impacts of the microalgae cultivation process integrated on the AD effluent are identified:

• Reclamation of the environmental and economic value of the wastewater effluent in terms of

water and nutrient recovery;

• Recycle of large volumes of water for on-site and off-site uses;

• Generation of an algae biomass product that is suitable for on-site reuse, energy generation or

for sale to available markets;

• Sequestration of carbon dioxide currently generated by AD reactors during the current

wastewater treatment process and fixation into algae biomass.

The promising outcomes of this technology assessment pave the road for further and more detailed

explorations that aim at improving technical understanding, environmental and economic footprint

and potential for full-scale applications. Experimental test works on microalgae cultivation on

abattoir wastewaters are deemed essential to corroborate, improve and expand the techno-

economic assessment developed in this project. Recommendations for future R&D projects include

bioprospecting studies through a pilot plant implemented at the premises of an operating Australian

abattoir. Through long-term outdoor experiments, microalgae species suitable for growing on

abattoir wastewaters are identified, together with the most cost-effective cultivation and harvesting

methods, impacts of seasonal variations of inflow streams and nutrient supplies on algae growth

rates. The optimization of microalgae growth conditions for maximum nutrient removal and the

evaluation of different microalgae sources for animal/aquaculture feed is also an expected outcome

of a bioprospecting study. As highlighted by the sensitivity analysis, it is recommended to carefully

address the impacts of algae productivity per unit area and effluent composition (i.e., flow rate and

nutrient content) on the overall system performances through extensive experimental test work at

pilot scale.

2.0 INTRODUCTION

Australia is amongst the global leaders in the export of red meat and livestock, contributing A$17

billion to Australian economy. The global demand for meat has constantly been increasing,

encouraging the industry to develop more sustainable food systems while meeting social

responsibilities. In light of more competitive global markets, rising energy prices, and environmental

responsibilities, the industry has aimed to improve environmental credentials of their business, while

enhancing economic efficiency.

Red meat processing facilities generate large volumes of wastewater and solid waste rich in organic

contaminants. Through “waste-to-profit” initiatives and research, these streams can be strong

candidates for treatment processes aiming at the recovery of energy and nutrient resources and for

the production of value-added products. The proposed project will investigate the integration of

microalgae cultivation in the red meat processing facilities as a new process technology towards

water treatment, reuse and recycle. The project identifies different sources of water and effluents

from solid waste and wastewater treatment in meat processing facilities and evaluates their

potential for utilization in a microalgae cultivation process. The cultivation is conducive to purifying

the waste streams and production of value added products such as biofuel, cattle feed, and high

value pigments. The viability of treated water recycling within meat processing operations is

assessed, whilst taking into consideration food safety standards and associated risks. An economic

assessment of the proposed system is conducted based on the mathematical model developed in the

study. The concept model of the proposed integrated algae cultivation is drafted in Figure 1.

Anaerobic digestion (AD) effluents, primarily treated wastewater, raw wastewater, runoff water and

alternative water sources generated during meat processing operations are all addressed as potential

targets of the proposed microalgae cultivation system. Microalgae have the ability to recover

nitrogen and phosphorous from wastewater streams and to sequester the carbon dioxide currently

generated by AD processes in abattoirs into algae biomass. The resulting product is clean water and

microalgae biomass, both valuable products potentially improving the environmental footprint and

economic benefits of the meat processing facility.

This project addresses specific industry needs related to the challenges with the management and

treatment of wastewaters produced in abattoirs. The environmental impacts and costs related to the

production of large volumes of waters that are high in nutrients, pathogens and organic content

represent a critical burden meat processing facilities are currently facing. The application of

microalgae cultivation for nutrient removal represents a reliable and mature technology widely

applied in the context of wastewater treatment. Moreover, due to the availability of abundant solar

resources and land, Australia is considered as one of the best locations for microalgae cultivation

systems. Although not yet applied to treat abattoir wastewaters, recent studies conducted at

Murdoch University have been successful in growing three high ammonium resistant species of

microalgae on undiluted AD piggery effluents. This research represents a proof-of-concept study that

illustrated the potential of culturing microalgae in such a very turbid and high ammonium

wastewater. To this end, abattoir AD effluents are expected to be a more suitable algae growing

substrate than piggery effluents due to lower turbidity and nitrogen content. In the context of red

meat processing facilities, the integration of microalgae cultivation system as proposed in Figure 1 is

expected to:

• Reduce liquid waste streams, associated treatment and disposal costs by producing a clean

wastewater effluent for safe discharge;

• Provide potential for treated wastewater effluents to be reused and recycled within abattoir’s

operations;

• Reduce the environmental impacts of the abattoir by reducing freshwater consumption,

promoting water recycling, reducing the carbon footprint by lowering greenhouse gas

emissions;

• Generate additional revenue streams by using the cultivated algae biomass as animal feed,

energy source as biogas, fertilizer and high-value pigments;

• Fully integrate a “waste-to-profit” concept through the recovery of valuable resources (i.e.,

water and nutrients) from wastewaters.

Figure 1. Integration of microalgae cultivation with the wastewater treatment process.

3.0 PROJECT OBJECTIVES

The five overarching project objectives as specified in the signed Agreement are listed below:

1. Identify the potential approaches for the use of alternative water sources (including the

effluents from a microalgae cultivation process) in meat processing facilities.

2. Investigate a new technological approach for the transformation of nutrient contents in red

meat processing wastewater (and solid waste) streams into protein rich biomass via microalgae

cultivation.

3. Identify new potential for water reuse in meat processing facilities (including reuse in the

proposed microalgae cultivation system).

4. Investigate new approaches for water recycling (including the algal-treated water recycling

opportunities).

5. Assess the environmental and economic performance of the proposed water management

system.

Each objective has been addressed progressively by defining six major project milestones, each

focusing on specific project deliverables:

1. Milestone 1. Literature review and data collection

(i) Review of food safety standards applicable to the meat processing industry

(ii) Collection of water sources, use, collection, and treatment data from large-scale meat

processing facilities for the development of case studies

2. Milestone 2. Literature review on microalgae systems

(i) Review of microalgae cultivation systems and applications in meat processing industry

(ii) Review of existing water sources, use, collection, effluent treatment processes including

existing anaerobic digestion, runoff water, and nutrient removal systems for comparison

with the proposed micro-algal integrated process

3. Milestone 3. Alternative water sources identification and waste water quality assessment

(i) Characterizing existing water sources, use, and waste collection (based on the potential for

the integration of microalgae cultivation process)

(ii) Identification of alternative water sources

(iii) Assessment of waste streams quality (nutrient content) and suitability for algae cultivation

process.

(iv) Assessment of flow quantities to be used as input for system sizing.

(v) Reconfiguration of water/waste water streams considering the integration of microalgae

cultivation into the process.

4. Milestone 4. Algae-cultivation system design

(i) Determination of microalgae cultivation approaches based on wastewater streams

identified

(ii) Development of a mathematical model representing the operation of microalgae

cultivation on AD effluents, water runoff and identified water/waste water streams

identified (mass and energy balances)

5. Milestone 5. Environmental impact analysis

(i) Environmental impact assessment (consequential analysis): investigating the environmental

performance of the proposed microalgae treatment system in comparison with

conventional treatment process used in the sample plant

(ii) Food safety risk assessment and system enhancement

6. Milestone 6. Cost benefit and uncertainty analysis

(i) Cost benefit analysis for the proposed microalgae cultivation system

(ii) Sensitivity and uncertainty analysis

4.0 METHODOLOGY

4.1 Literature review and data collection

As an R&D desktop and modelling project, the review of the published literature produced by the

scientific community worldwide in the form of scientific papers, books and conference publications is

central to the project methodology. Review of previous and current work developed at Murdoch

University (e.g., Ayre et al., 2017; Chaudry et al., 2017; Nwoba et al., 2016; Borowitzka and

Moheimani, 2013; Moheimani 2005) and by R&D MLA/AMPC projects (Hamawand et al., 2015;

Ridoutt et al., 2015; Jensen and Batstone, 2012; Jensen and Batstone, 2013) constitutes in-house

background knowledge and a substantial source of information, particularly in regards to data on

Australian abattoirs. About 30 AMPC/MLA reports have been reviewed to achieve the objectives of

Milestone 1. Major attention was given to recent reports, published in the last five years, in order to

capture the latest trends and innovations achieved by the red meat industry in Australia. The review

by Bustillo-Lecompte and Mehrvar (2015) was used as the reference work in regards to the recent

trends and advances on the characterization and treatment of abattoir wastewaters worldwide.

Information on food safety standards and regulations was collected through personal communication

with export-registered abattoirs, MLA and AMPC, the Department of Agriculture and Water

Resources, the Department of Health, and the Office of the Environmental Protection Authority.

Two AMPC reports (Jensen and Batstone, 2012; Jensen and Batstone, 2013) and personal

communication with the reports’ authors have provided access to a large amount of information and

data on six Australian abattoirs (hereafter referred to as Sites A to F). Personal communication

between Murdoch University and another abattoir (hereafter referred to as Site G) has provided

access to the abattoir’s data on wastewater production and treatment. The level of detail of the

collected data varies for each abattoir depending on data availability, confidentiality agreements,

abattoir’s operations and routine monitoring policies. An in-depth review of the data available at

each site is reported in Appendix 9.1. For the purpose of this project, a comprehensive dataset is

available for three abattoirs only, while other abattoirs supplied partial and/or inaccurate

information. Out of the seven reviewed abattoirs (Appendix 9.1), Sites A, D and G have been selected

as the most appropriate ones to develop the mathematical model as they provide the most

comprehensive and reliable set of data. There are substantial differences between Site G dataset and

the data available at Sites A and D. Site G data are taken at different sampling points within the

abattoir’s wastewater treatment plant and are generated by routine monitoring programs over a

long-time period (three years of routine monitoring). The data published by Jensen and Batstone

(2012, 2013) on Sites A and D are taken at different sampling points within the slaughtering process,

as opposed to within the abattoirs’ wastewater treatment plant like at Site G, and were measured

during a monitoring campaign of intensive sampling lasting a few days (as opposed to the three-year

dataset provided by Site G). Available data on Sites A and D thus represent an instantaneous picture

of the abattoir’s operations rather than its continuous operations. For these reasons, a direct

comparison between Site G and Sites A and D is not entirely meaningful and appropriate, and the

two sets of abattoirs are presented and analyzed separately.

Major upgrades occurred at Site A and D after the work of Jensen and Batstone (Jensen and

Batstone, 2012; Jensen and Batstone, 2013). A new covered lagoon was installed at Site A aiming at

collecting and re-using the biogas produced by anaerobic digestion (AD). An upgraded system for

blood collection was installed at Site D which contributed to lower the nitrogen concentration in the

wastewater by about 30% the value measured by Jensen and Batstone in their 2013 MLA/AMPC

report. The data used in the present project refer to the pre-upgrade conditions at Sites A and D.

Also, Sites A and D show many similarities in size, location, wastewater composition, handling and

treatment. Site A is located in Southern Queensland and Site D is located in Northern New South

Wales, with a distance of only about 200 km between the two abattoirs. Both abattoirs are similar in

size (about 1,000 heads processed daily) and the composition of the treated wastewater after AD is

very similar. Because of these similarities, although both sites have been presented and analyzed

separately for most of the project, major attention in terms of mathematical modelling, cost analysis

and discussion has been given to Site D. The same data interpretation and process conclusions are

applicable to Site A.

4.2 Mass balance of the microalgae cultivation system

The mass and energy balances of the integrated microalgae cultivation process have been developed.

Amongst the reviewed Australian abattoirs, three sites have been selected for modelling, namely

Sites A, D and G. Those sites have been selected because a comprehensive set of data which includes

pre and post AD characterization and wastewater flow rates across the abattoir is available.

The approach used in the calculation of the mass and energy balances is explained hereafter. The

values of modelling parameters such as algal productivity and energy consumption rates are taken

from recent experimental and modelling studies on microalgae cultivation systems. Note that the

modelling parameters related to microalgae dynamics (e.g., growth, settling) refer to experimental

values on the cultivation of the microalgae Chlorella which has been shown to grow reliably on

challenging substrates and conditions (Ayre et al., 2017; Ras et al., 2011). The uncertainty associated

with the modelling assumptions and input data represents the main source of error and is addressed

by an appropriate sensitivity analysis.

The mass balance of the microalgae cultivation system aims at quantifying the concentrations and

mass fluxes of all the components involved in the process. The components involved in the growth of

microalgae are water, sunlight, carbon dioxide, and some nutrients, mainly nitrogen and phosphorus.

The photosynthetic reaction that takes place in a microalgae cultivation system is described by Eq. 1,

where C106H263O110N16P is the approximate chemical formula for microalgae estimated from the

Redfield Ratio (Borowitzka and Moheimani, 2013).

21611026310624232 1381712216106 OPNOHCHOHPOHNOCO light Eq. 1

The selection of an appropriate wastewater stream to be integrated with a microalgae cultivation

system was the specific deliverable of Milestone 3 report (refer to Section 5.3 and Appendix 9.3) and

the AD effluent stream resulted to be the most appropriate due to its low concentration of organics

and high nutrient content. Based on the composition and flow rate of the AD effluent stream, a daily

flux of nitrogen, phosphorus and carbon dioxide is calculated. Whilst the amount of nitrogen and

phosphorus available to grow algae is provided by the wastewater itself, the amount of carbon

dioxide available to the process is assumed to be recycled from the AD process. It is assumed that the

methane produced in the AD pond is burnt (following the combustion reaction described in Eq. 2),

and the resulting CO2 is recycled as input to the microalgae cultivation system. Although the biogas

produced by the AD pond at Site G is not currently captured, personal communication with Site G

personnel has confirmed on-site methane capturing and combustion as one of the abattoir’s short-

term priority. In the following mass and energy balance calculations, it is therefore assumed that CO2

is available at Site G by AD biogas combustion.

OHCOOCH 2224 22 Eq. 2

The three components needed for algal growth, i.e., carbon dioxide, nitrogen and phosphorus, are

not expected to be in perfect balance, therefore one component (usually nitrogen or phosphorus) is

likely to be limiting the biomass growth. The limiting component is determined by the stoichiometric

ratio of each component to one another as well as the theoretical ratio in the Redfield equation, i.e.,

C:N:P = 106:16:1 (Eq. 1). This ratio is applied to the molar concentrations of each component. Based

on the calculation of the limiting component and the Redfield stoichiometry, the theoretical amount

of algae biomass that can grow on the selected wastewater stream is calculated. The fractions of

nutrients and carbon dioxide that have not been used for algal growth are also calculated as the

difference between the incoming flux and the amount of nutrients and carbon dioxide fixed in the

algae biomass. Once the theoretical amount of biomass is calculated and assuming a typical

productivity of the microalgae cultivation system from literature values (25 g/m2/d, annual average,

Collet et al., 2011; Ayre et al., 2017), the size of the microalgae cultivation system is estimated. After

the cultivation phase, the biomass is harvested and dewatered before final use. It is considered that

the biomass is harvested on a daily basis at the same rate at which it grows. The harvested stream

from the algae pond is highly diluted and a typical algae concentration is considered at 0.5 g/L (0.05%

solids, Collet et al., 2011). Natural settling followed by centrifugation can achieve algae

concentrations at 30% solids, thus preparing the algae biomass for further dewatering and drying

whether the final biomass is to be transported for off-site uses. A 90% efficiency of the dewatering

process is considered (Chaudry et al., 2017).

During the cultivation phase in open ponds, a significant amount of water is expected to be lost by

evaporation, thus a quantification of the evaporative flux is also required (Eq. 3):

WEVEV ARF Eq. 3

Where FEV is the evaporative flux (kL/d), REV is the rate of evaporation (cm/d), A is the area of the

cultivation system (m2), and ρW is the density of water (kg/m3). An amount of water that is equivalent

to the volume lost by evaporation is required to be continuously added to the microalgae cultivation

system to make up for evaporation losses. The water resulting from the dewatering step is

appropriate for recycling into the growth ponds to make up for evaporation losses.

A schematic representation of the mass balance of the microalgae cultivation process is shown in

Figure 2. This mass balance represents the base case and generates two product streams (Figure 2): a

30% solids microalgae biomass and a nutrient-depleted water effluent. The values of parameters and

constants used in the mass balance calculations are summarized in Table 1. Note that values refer to

raceway ponds as the microalgae cultivation system of choice in this project. The choice of raceway

open ponds over closed photobioreactors is further discussed in Section 5.4.1.

Figure 2. Schematic representation of the mass balance.

4.3 Energy balance of the microalgae cultivation system

The energy balance aims at quantifying the energy inputs and outputs associated with the

microalgae cultivation system. The main energy output is related to the amount of energy contained

in the dry algal biomass and is quantified by the calorific value of the biomass itself (Table 1). The

energy inputs are related to the energy demand of cultivation process, harvesting and dewatering of

algae biomass.

The amount of energy required by the cultivation process is most entirely related to the mixing of the

system by the paddlewheel mechanism. Its quantification is given by Eq. 4, where ECUL is the energy

input to the cultivation system (kWh/d), ERPW is the energy demand by the paddlewheel mixing

system (kWh/ha/d), A is the area of the cultivation system (ha), and OD is the operating days (d).

Note that, as a strategy to reduce energy consumption, recent experimental tests conducted at

Murdoch University have demonstrated the feasibility to operate the paddlewheel mixing

mechanism during the day only (12 hours per day) instead of continuous operations. Although a 12

hour/day operation of the paddlewheel mixing process is possible, a 24 hour process is considered

hereafter as a high range estimate of energy demand.

ODAERE PWCUL Eq. 4

No energy is required for natural settling of the harvested biomass; however, dewatering by

centrifugation at 30% solids is an energy intensive process. Collet et al. (2011) assume an energy

demand of the centrifugation step at a loading rate of 7 to 10 g/L of biomass equal to 1 MJ/kg of

biomass. Whether a lower solid content is required (i.e., 5% solids), the energy demand decreases to

0.15 MJ/kg of biomass (Collet et al., 2011). The amount of energy required for dewatering is

expressed by Eq. 5

waterDEWDEW FERE Eq. 5

Where EDEW is the energy required for dewatering (kWh/d), ERDEW is the energy consumption per

kilogram of algae biomass to dewater (kWh/kg), and Fbiomass is the daily flux of harvested biomass

(kg/d).

Energy supply is also required for water and carbon dioxide pumping. The values of energy

consumption rates suggested by Collet et al. (2011) and Chaudry et al. (2017) have been used in the

energy balance (Table 1). Note that the energy required for pumping the algae inoculum to the pond

system and the energy associated with wastewater pumping throughout the system are considered

negligible comparing to the energy demands of mixing and dewatering. Whether a pilot system is to

be designed, the energy rates associated with pumping water and algae streams are to be included in

the energy balance.

Table 1. Values of parameters and constants for mass and energy balances.

Parameter/constant Value Reference

Mass Balance

Algal productivity in open ponds (g/m2/d) 25 Collet et al., 2011; Ayre et al., 2017

Depth of raceway ponds (m) 0.30 Collet et al., 2011

Rate of evaporation REV (cm/d) 0.4 BoM Australia

Density of water ρW (kg/m3) 1,000 -

Density of biomass ρbiomass (kg/m3) 1,000 Chaudry et al., 2017

Energy Balance

Calorific value of 90% solids algae biomass (kWh/kg)

3.5 – 4 Ghayal and Pandya, 2013

Energy demand by the paddlewheel mixing ERPW (kWh/ha/d)

48 Chaudry et al., 2017

Energy demand by dewatering (kWh/kg) 0.04 – 0.3 Collet et al., 2011

Energy demand by pumping water (kWh/m3) 0.05 Collet et al., 2011

Energy demand by pumping CO2 (kWh/kgCO2) 0.021 Chaudry et al., 2017

Operating days per year OD (d) 330

4.4 Environmental impact assessment

One of the project objectives aims at determining the environmental impact and risk assessment of

the integrated microalgae cultivation process in comparison with the wastewater treatment

currently implemented at the selected abattoirs. The assessment of risks associated with the

identified environmental hazards is related to the composition of the wastewater effluents and algae

cultivation products (i.e., nutrient-depleted water effluent and algae biomass) estimated by the mass

and energy balances. The uncertainty associated with the calculation of the mass balance is going to

impact on the results of the environmental impact assessment. For this reason, the assessment

discussed in this project is considered a high-level evaluation of environmental impacts and risks. A

full environmental impact assessment integrated with an appropriate life cycle analysis is

recommended once an ad-hoc experimental campaign provides more data and understanding of the

integrated microalgae cultivation process (e.g., bio-prospecting study).

A qualitative characterization of the environmental impacts and associated risks is determined by

following the procedure described in Chapter 4 of the Australian Guidelines for Water Recycling,

hereafter referred to as AGWR (2006). Table 2.7 of the AGWR (2006) is used to estimate the risk by

defining likelihood and consequence of each identified environmental hazard. The main

environmental endpoints are combined with the key hazards, the intended uses of the wastewater

effluent and their identified environmental impacts to determine the severity of the associated

environmental risks. A ‘low’ risk is defined as acceptable by the AGWR and does not require

preventative measures. ‘Moderate’ to ‘Very High’ risks require intervention to reduce the risk levels

to acceptable. In this study, major attention is given to hazards caused by high concentrations of

nitrogen and phosphorous when the treated abattoir wastewater is discharged into storage ponds

and/or recycled for the on-site and off-site uses permitted by the AGWR (e.g., irrigation, fire control,

and wash down of tracks and yards). Nitrogen and phosphorus are included in the nine key

environmental hazards to be considered in risk assessment studies when the treated wastewater is in

contact with environmental endpoints such as soils, surface waters and groundwater (AGWR, 2006).

The concentration of nutrients in the final wastewater effluent is the main target of the proposed

microalgae cultivation system when compared to traditional wastewater treatment process, thus

making the focus on nutrient concentrations particularly significant for the current project. Other key

environmental hazards to be analyzed in a full environmental impact assessment include boron,

cadmium, chlorine disinfection residuals, hydraulic loading, salinity, chloride, sodium, and microbial

content (AGWR, 2006). Together with nutrient concentrations, those hazards will determine the

suitability of the final effluent to be recycled in the abattoir’s operations.

4.5 Cost-benefit analysis of the microalgae cultivation system

The report by worldwide renowned algae expert John Benemann (Lundquist et al., 2010) on the

economics of microalgae cultivation in open raceway ponds is used as the main reference for the

cost-benefit analysis developed in this project. This report is a highly detailed economic analysis of a

microalgae cultivation system coupled with a wastewater treatment plant to treat wastewaters

produced by farming and agriculture activities. Similar to our current application of microalgae to

treat abattoir’s wastewaters, the emphasis is on the wastewater treatment side with the algae

biomass being a valuable by-product. The unit costs reported by Lundquist et al. (2010) are defined

per hectare and refer to 2010 US dollars. An AU to US dollars conversion rate of 1.3 and an US

inflation rate of 1.12 (based on 2017 and 2010 Consumer Price Index equal to 244 and 218,

respectively, CPI website) are considered to convert 2010 US dollars into 2017 AU dollars. Costs

associated with inoculum cultivation, labor, engineering fees, contingencies and taxes are sourced

from Wijihastuti (2017) and are representative of 2017 Australian conditions. All unit costs used in

the cost-benefit analysis are summarized in Table 2.

Table 2. Summary of capital and operational costs.

Value Unit Reference

Capital Costs

Open raceway pond – clay lined 34,100 2010 US$ / ha Lundquist et al., 2010

Buildings, roads, drainage, vehicles 4,610 2010 US$ / ha Lundquist et al., 2010

Electrical 19,000 2010 US$ / ha Lundquist et al., 2010

Water piping 14,000 2010 US$ / ha Lundquist et al., 2010

CO2 (flue gas+ distribution) 5,940 2010 US$ / ha Lundquist et al., 2010

Dewatering system 12,130 2010 US$ / ha Lundquist et al., 2010

Digesters 21,900 2010 US$ / ha Lundquist et al., 2010

Biogas turbine 24,400 2010 US$ / ha Lundquist et al., 2010

Inoculum system 15,996 2017 AU$ Wijihastuti, 2017

Standardized indirect capital costs

Engineering fees 15% of capital % Wijihastuti, 2017

Contingency 5% of capital % Wijihastuti, 2017

Working capital 5% of total capital % Wijihastuti, 2017

Operational costs

Electricity 0.27 AU$/kWh

Labour - Plant Manager 113,520 2017 AU$/year Wijihastuti, 2017

Labour - Engineer 84,480 2017 AU$/year Wijihastuti, 2017

Labour - Lab Analyst 63,360 2017 AU$/year Wijihastuti, 2017

Labour - Administration 60,720 2017 AU$/year Wijihastuti, 2017

Labour - Technician/Pond Operator 50,160 2017 AU$/year Wijihastuti, 2017

Maintenance/ Insurance 10% of total capital % Wijihastuti, 2017

Tax 27.5% of total capital % Wijihastuti, 2017

4.6 Sensitivity and uncertainty analysis

A sensitivity analysis was conducted to identify how the uncertainty associated with the modelling

assumptions can impact the system’s performance. The modelling assumptions subjected to

sensitivity analysis are related to the characterization of the AD effluent (i.e., nutrients concentration

and AD effluent flow rate), algae productivity per unit area, specific energy requirement for pond

mixing and dewatering as the main energy demanding processes, capital costs associated with pond

construction, harvesting system and other capital costs lumped together (buildings, roads, water

piping, electrical system). The system’s performance affected by the modelling assumptions is

related to the daily amount of harvested biomass, the daily flow rate of recycled nutrient-depleted

water, algal pond size, total capex and opex, and algae production unit costs.

Table 3 summarizes the base case values assumed in the mass and energy balance calculations and

the deviation from base case as evaluated in the sensitivity analysis. A 50% variation at 25%

increments has been chosen for the concentration of nutrient and flow rate in order to capture the

variability observed at the different sites. The three-year dataset provided by Site G has shown a ±

25% variation from the average concentration of total nitrogen and phosphorus, thus the sensitivity

analysis at ± 50% is expected to cover the wastewater composition variability as measured on site. A

greater than 50% variation of the flow rate could occur at Site G; however, the absence of historical

flow rate data due to a poor monitoring system does not allow a more specific estimate of the post

AD wastewater stream. The 50% variation of algae productivity takes into account the seasonal

variability of algae growth, with summer peaks at 40 g/m2/d and winter minima lower than 10

g/m2/d. Opex and capex have been varied from -25% to +100% at 25% increments to take into

account the large variability of the modelling assumptions related to the system’s costs.

Table 3. Base-case values and percentage variation of the modelling parameters tested by sensitivity analyses.

Modelling parameter Base case Variation from base case (%)

Wastewater characterisation

Nitrogen concentration (mg/L) Site D: 229; Site G: 151 -50; -25; +25; +50

Phosphorous concentration (mg/L) Site D: 32; Site G: 26 -50; -25; +25; +50

AD effluent flow rate (kL/d) Site D: 2,150; Site G: 1,750 -50; -25; +25; +50

Algae growth

Algae productivity (g/m2/d) 25 -50; -25; +25; +50

Operational costs

Specific energy for pond mixing (kWh/ha/d) 48 -25; +25

Specific energy for dewatering (kWh/kg) 0.3 -25; +25

Capital Costs

Open raceway pond – clay lined (2017 AU$ / ha) 49,620 +25; +50; +100

Dewatering system (2017 AU$ / ha) 17,651 +25; +50; +100

Others (2017 AU$ / ha) 79,367 +25; +50; +100

5.0 PROJECT OUTCOMES

5.1 Milestone 1. Literature review and data collection

5.1.1 The red meat processing industry and its environmental impacts

The red meat processing industry in Australia comprises of around 191 sites (i.e., individual facilities)

spread across 120 businesses (Hamawand, 2015). A process flow diagram of the operations that

typically occur in abattoirs is summarized in Figure 3 (COWI, 2000). Cattle are delivered to the

abattoir in trucks and unloaded into holding pens, where they are washed before slaughter. After

stunning, bleeding takes place with the blood being collected in a trough for disposal or for further

processing. The bled carcasses are conveyed to the slaughter hall where dressing and evisceration

take place. Once the edible and inedible offal are separated and the carcass has been washed, it is

sent to a cold storage area for rapid chilling. Carcass cutting and boning often take place after chilling

and a following inspection of carcasses and viscera ensure they are suitable for human consumption.

At various stages in the process, inedible by-products such as bone, fat, heads, hair and condemned

offal are generated. These materials are sent to a rendering plant either on site or off site for

rendering into feed materials. Of the average 600 kg live cattle weight, about 45% becomes the final

meat product, another 30% is inedible material for rendering (bone, fat, heads, hair and condemned

offal), 8% and 6% are hide and edible offal, respectively, 7% is blood and the remaining 4% is

constituted by paunch manure, blood loss and other losses (COWI, 2000; Jensen and Batstone, 2012).

Red meat processing facilities critically depend on water and energy for their operations. The average

total energy consumption of an abattoir is about 3,000 MJ per ton of hot standard carcass weight

(tHSCW) as reported by the 2015 AMPC environmental performance review report (Ridoutt et al.,

2015). High level of thermal energy in the form of steam and hot water is routinely used for cleaning,

sanitizing and rendering. Approximately 80-85% of the total energy need of an abattoir is for thermal

energy, with the remaining being electricity used for the operation of machinery and for

refrigeration, ventilation, lighting and the production of compressed air (COWI, 2000). Rendering

operations are normally the largest consumer of energy.

Figure 3. Process flow diagram of red meat processing operations. Operations with a substantial water consumption rate are highlighted in blue (COWI, 2000).

Within the food and beverages industry, the meat processing industry is the largest consumer of

water (Bustillo-Lecompte and Mehrvar, 2015). Water is mainly used for watering and washing of

livestock, washing of animal products (e.g., casings, offal, and carcasses), washing yards, trucks,

unloading areas and stock floors, cleaning and sanitizing of equipment and processing areas. The

operations that require large water volumes and the partitioning of water consumption are

highlighted in Figure 3. In their book on meat processing, COWI (2000) refers to a water consumption

that ranges from 4 to 15 kL/tHSCW. The World Bank Group states that a slaughterhouse plant can

consume between 2.5 and 40 kL of water per metric tons of meat produced (Bustillo-Lecompte and

Mehrvar, 2015). Following the adoption of new protocols and technologies that promote water use

efficiency and water recycling programs (e.g., weekly benchmarking of site water use efficiency,

reuse of sterilizer water, installed additional water meters and timers to better understand water

flows, use of recycled water for lawns, washing cattle, cleaning yards and screens), the consumption

of water in Australian processing plants has reduced significantly. From 16.6 kL/tHSCW in 1978,

water consumption in abattoirs reduced to a range from 2.8 kL/tHSCW for small plants processing

less than 1,500 tons of HSCW per week, to 8.6 kL/tHSCW for large export-registered plants (Ridoutt

et al., 2015; Hamawand, 2015). In their annual performance review of the 2013/2014 operations,

AMPC confirmed a water intake varying between sites from 5.7 to 12.7 kL/tHSCW cattle equivalent.

The water consumption is indicatively partitioned as follows (Ford, 2013): 25% of the total water

consumption is used for slaughtering, 22% for plant cleaning, 20% for stockyards and trucks washing,

13% for render and service, 10% for sterilizing, and 10% for paunch, gut and offal processing. Town

water is the most important source of water intake, followed by bore water, local dams, direct

withdrawal from a river, and rooftop rainwater harvesting as minor sources. Out of the 14 facilities

reviewed by AMPC in a 2013-2014 survey, 13% of the water demand was met by recycled water as 5

of the 14 sites reported using recycled water (Ridoutt et al., 2015). The source of recycled water is

commonly the treated wastewater effluent. Depending on the final use of the recycled water, the

stage at which wastewater is treated varies from pre-treatments by screening and floatation to more

advanced secondary and tertiary treatments, until possibly achieving potable standards. The most

common uses of recycled water consist in on-site and off-site irrigation, watering gardens, flushing

toilets, and washing down external areas.

The red meat processing industry is a substantial producer of wastewater streams that are rich in

nutrients and organic matter. The average site wastewater production has been reported as 8.5

kL/tHSCW (Ridoutt et al., 2015), which is nearly as high as the average water intake of 8.6 kL/tHSCW

(Ridoutt et al., 2015). Although some water is held up with by-products and/or lost through

evaporation, local rainfall is an additional source of water that adds to the water balance. It should

be noted that the quality of wastewater is highly dependent on the presence of on-site rendering

activities: although rendering only consumes about 5% of the total water requirements, the organic

strength of the generated wastewater is extremely high and contributes to about 60% of the total

organic load. Treatment of wastewater is almost always needed to ensure compliance with the

existing guidelines for safe discharge into sewer and/or water bodies and on-site recycling.

5.1.2 Wastewater characterization and treatment

The organic content of wastewater generated by Australian facilities is extremely high (5,000-10,000

mg/L COD) with nitrogen levels generally at 5% of COD concentrations and solids representing

approximately 70% of the total COD (Jensen and Batstone, 2012; Jensen and Batstone, 2013).

Slaughterhouse wastewater characterization as reported in recent review papers (Jensen and

Batstone, 2012; Bustillo-Lecompte and Mehrvar, 2015) is summarized in Table 4. The composition is

indicative and it can vary considerably: a concentration of Fat, Oil and Grease (FOG) as high as 1,780

mg/L has been reported by AMPC in a recent annual report (Ridoutt et al., 2015).

Of the seven abattoirs reviewed in this project (hereafter referred to as Sites A to G, Appendix 9.1),

Table 5 summarizes the composition of the combined wastewater at each study site. In general the

concentration (and load) of organic compounds are greater, or at the higher range, than the reported

literature values, while nutrient values are within the range of literature data. The consumption of

water varies across the sites and it is consistent with the estimate given in the latest AMPC report

(Ridoutt et al., 2015) equal to 8.6 kL/tHSCW. Water consumption at Site G is based on an estimate

expressed as kL of water per head per day, as the exact measurement is unavailable (personal

communication with the abattoir’s operator). A detailed review of each abattoir’s process flowsheet,

wastewater treatment process and available data is given in Appendix 9.1.

Table 4. Characterization of wastewater generated by red meat processing operations.

Concentration

(mg/L)a Load

(kg/tHSCW)b Load

(kg/head)b Load

(kg/t live)b

COD 500 – 15,900 16.7 – 44.4 6 – 16 10 – 26.7

BOD 150 – 4,635

TSS 270 – 6,400 9.3 – 22.2 3 – 8 5 – 13.3

TN 50 – 841 1.4 – 4.2 0.5 – 1.5 0.8 – 2.5

TP 25 – 200 0.1 - 0.4 0.05 – 0.15 0.1 – 0.3

FOG 270 – 1,800c 2.8 – 13.9 1 – 5 1.7 – 8.3

pH 4.90 – 8.10 a Bustillo-Lecompte and Mehrvar, 2015

b Jensen and Batstone, 2012

c COWI, 2000; Ridoutt et al., 2015

Table 5. Characterization of wastewater at the reviewed abattoirs, and comparison with literature data. NA: not available data.

Site (capacity) Water

(kL/tHSCW) COD

(mg/L) TS

(mg/L) FOG

(mg/L) TN

(mg/L) TP

(mg/L)

Literature 5.6-22.2 500-15,900 270-6,4001 100-600 50-841 25-200

Site A (800-1,200 heads/d) 8.1 12,893 8,396 2332 245 53

Site B (NA) 7.4 9,587 4,300 783 232 50

Site C (NA) 14.7 10,800 7,530 3350 260 30

Site D (800-1,400 heads/d) 11 12,460 7,400 1500 438 56

Site E (3,000 heads/wk) 7.1 10,925 6,118 1569 272 47

Site F (NA) 7.1 7,170 3,806 1915 182 27

Site G (500 heads/d) 2-5

kL/head/d 587 ± 440 (as BOD)

1,652 ± 1,0111

395 ± 413

123 ± 62 25 ± 14

1 TSS measurement

The treatment of abattoir wastewaters comprises a series of processes that aim at reducing the

concentration of organics, nutrients and pathogens to levels that are acceptable for discharge into

sewer or freshwater bodies. Wastewaters are commonly pre-treated by screening, settling, blood

collection, and fat separation, followed by physicochemical treatments, including dissolved air

floatation (DAF) and coagulation/flocculation, aiming at removing FOG and solids. Secondary

biological treatments (aerobic and/or anaerobic processes) aim at reducing the soluble COD and

nutrient concentrations. Although the organic matter and nutrient removal can achieve high

efficiencies, further treatment by membrane technologies and advanced oxidation processes are

normally required to achieve strict discharge guidelines. A summary of the most common

wastewater treatment processes used by the meat processing industry is shown in Figure 4 (Bustillo-

Lecompte and Mehrvar, 2015).

Figure 4. Abattoir wastewater treatment process.

The following processes are the most conventional ones found in the reviewed abattoirs Sites A to G:

• Preliminary treatments: solids screening. Solids are normally separated from the wastewater

and sent to compost.

• Primary treatments: separation of solids and fats by saveall/DAF systems, where fats, oils and

grease are collected from the surface, whilst solids accumulate at the bottom.

• Secondary treatments: AD is extensively used to reduce the organic load of the wastewater.

Soluble organic materials are converted to volatile acids, carbon dioxide, hydrogen and bacteria

cells during anaerobic processes. Volatile acids (mostly acetic acid) and other products are then

converted to methane and carbon dioxide by methane-producing bacteria. During this stage,

nitrogen is released as ammonium nitrogen, thus the nutrient removal by AD does not often

achieve nutrient concentrations within regulation limits.

• Secondary treatments: aerobic treatments based on denitrification-nitrification for nitrogen

removal are used to reduce the organic as well as nitrogen load. Organic load is converted to

bacterial biomass, whilst ammonium nitrogen is converted to nitrate and to gaseous nitrogen by

heterotrophic bacteria.

Table 6 summarizes the efficiency of different processes (mostly anaerobic and aerobic processes)

for the removal of COD, BOD and total nitrogen from abattoir wastewaters. Table 6 originates from

the table published by Bustillo-Lecompte and Mehrvar (2015) and is adjusted to reflect those

wastewaters characterized by COD concentrations representative of Australian meat processing

plants. The treatment efficiency of abattoirs wastewaters varies extensively; it depends on several

factors including, but not limited to, the characteristics of the wastewater, the hydraulic retention

time, and the pollutant concentration in the influent. Combined processes (e.g., anaerobic-aerobic

reactors, aerobic-membrane technology, coagulation/adsorption processes) are able to couple the

benefits of different technologies and have evolved into a reliable technology able to remove organic

compounds as well as nutrients. The selection of a specific treatment mainly depends on the

characteristics of the wastewater being treated, the best available technology, and the compliance

with current regulations under different political jurisdictions.

Table 6. Comparison of different processes for abattoir wastewater treatment (Bustillo-Lecompte and Mehrvar, 2015, and reference therein).

Processes1 HRT2 COD3 (mg/L) BOD3 (mg/L) TN3 (mg/L) COD

removal (%) BOD

removal (%) TN

removal (%)

AnaP 30-80 7,148-20,400 3,501-8,030

62-96 94

AnaP 24-48 7,083

547 94

AnaP 60 4,200-9,100

565-785 72-99

46-64

AnaP 30-97 8,450-41,900 21,000

19-57

AnaP 39-72 1,040-24,200

296-690 30

AnaP 24-36 2,273-20,073

570-1,603 51-72

3.5-22

AnaP 46-72 12,000-15,800

60

AnaP 48-72 1,014-12,100 1,410-7,020

84 94

AnaP 60-96 5,659-9,238 5,571-6,288

92-97 98-99

AeP 42 6,400-8,320

260-306 95

97

AeP

24,000 1,198 139 90

AeP 23 5,590-11,750 3,450-4,365 214-256 74-94

AeP 29 9,040 5,242

89 90

CC - 10,226-15,038 5,042-8,320

32-64 35-68

AnaP-MF 48-168 2,084-13,381

108-295 97-99

78-90

AnaP-AeP-CC 16-72 6,363-11,000 5,143-8,360 47-138 50-97 98-99 73-93

AnaP-AeP 24 6,000-14,500

300-1,000 99

46

1 AnaP, anaerobic process; AeP, aerobic process; CC, chemical coagulation; MF, membrane microfiltration 2 HRT, hydraulic retention time 3 Influent concentration of COD, BOD and total nitrogen

5.1.3 Food safety standards applicable to the meat processing industry

Food Standards Australia New Zealand (FSANZ) has developed a national food safety standard that

covers food safety management in the primary production and processing stages of the meat supply

chain. The meat processing is defined as a series of activities that include the admission of animals

for slaughter, dressing, boning, packing and production of meat and meat products. All States and

Territories have legislation that requires businesses operating abattoirs to be licensed or accredited

and to operate in accordance with approved systems to manage meat safety and suitability. The

safety of meat and meat products in Australia is currently implemented through reference to the

following Australian Standards (AS):

- AS4696-2007 Hygienic Production and Transportation of Meat and Meat Products for Human

Consumption

- AS 4466-1998 Hygienic Production of Rabbit Meat for Human Consumption

- AS 4467-1998 Hygienic Production of Crocodile Meat for Human Consumption

- AS 5010-2001 Hygienic Production of Ratite Meat for Human Consumption

- AS 4464-2007 Hygienic Production of Wild Game Meat for Human Consumption

In addition to the standards listed above, individual State Government Departments have set their

own State Food Health Acts that apply to the local markets of meat products. If meat products are

exported overseas, rules set by Quarantine and Export Control Meat and Meat Products Orders 2005

also apply. A list of the standards reviewed by the authors is summarized in Table 7.

Table 7. Food safety standards applicable to the meat processing industry.

Title Abbr.

Australia wide

• Primary production and processing standard for meat and meat products - Standard 4.2.3 - as of 31 July 2015

FSANZ, 2015a

• Proposal P1014 - Primary Production & Processing Standard for Meat & Meat Products

FSANZ, 2015b

• Australian standards for the hygienic production and transportation of meat and meat products for human consumption AS4696-2007

Browne, 2007

• Export Control (Meat and Meat Products) Orders 2005 - as of 1 Sep 2014

Export Orders, 2005

• AQIS Meat Notice 2008/06: Efficient use of water in export meat establishments

AQIS, 2008

Western Australia

• Food Act 2008 - as of 25 July 2016 Food Act, 2008

The Australian Standards AS4696 2007 (Browne, 2007) set the guidelines in relation to the quality of

the water used in the meat processing industry. The standards apply to the water withdrawn from

external water sources (e.g., municipal water supply reticulation) as well as to the water that is

recycled and reused after on-site wastewater treatment. The standard AS4696 2007 (Browne, 2007)

states that only potable water is permitted in all those activities that involve the direct contact with

the meat and meat products. Potable water needs to be sourced from safe potable water supply

reticulation systems that are protected from seepage from drains, sewerage, septic systems, manure

pits and other sources of contamination. The use of non-potable water is allowed in all those

circumstances where there is no risk of the water coming into contact with meat and meat products,

such as steam production, fire control, the cleaning of yards and the washing of animals other than

the final wash.

The use of recycled water by the meat processing industry has been seen as an effective way to

reduce fresh water consumption in meat processing facilities and operations, thus decreasing costs

relative to freshwater purchase and improve the industry’s environmental footprint. Recycled water

can be sourced externally; however it is more common to re-use the recycled water that is produced

in-house. To this end, the treated wastewater effluent is the most common source of recycled water.

In their review on Australian regulations for water recycling in the meat industry, CSIRO in

collaboration with AMPC and MLA found only little information on the safety standards regulating

the use of recycled water in meat processing facilities (CSIRO, 2014). This is attributed to loading

rates that are difficult to be assessed in the guidelines and local soil and climatic conditions needing

local assessment. In summary, the following guidelines apply to the use of recycled water in

abattoirs:

• Any water and recycled water used in the operations of the facility is to be kept away from

human or animal faecal contamination, or needs to be treated to an extent that the risk from

human sourced pathogens and chemical contaminants is controlled.

• If recycled water is to be used in meat processing operations, then it must be treated to potable

standards as required by the Australian Standards AS4696 2007 (Browne, 2007) and be

subjected to the risk assessment procedures Hazard Analysis Critical Control Point (HACCP). The

Australian Drinking Water Guidelines (NHMRC, 2011) are considered the document of reference.

Although treated to potable standards, the recycled water must not be used as a direct

ingredient in meat products or for drinking water at the processing facility (AQIS Meat Notice,

2008).

• Non-potable recycled water can be used for all purposes that do not involve meat productions

(e.g., irrigation, pre-wash of cattle and slaughter yard, fire control, the cleaning of yards and the

washing of animals other than the final wash, flushing toilets and watering gardens). In this case,

the Australian Guidelines for Water Recycling (AGWR, 2006) are considered the reference

guideline.

• Non-potable recycled water can be used as livestock drinking water for consumption by cattle

above 12 months of age, as defined by the AGWR (2006). In this case, additional water quality

objectives should ensure soluble BOD below 20 mg/L, suspended solids below 30 mg/L, E. Coli

less than 100 CFU (colony forming units) per 100 mL.

• Potable and non-potable recycled water may be used in export registered meat establishments;

however, processors must be aware that some countries, such as US, Middle East and Asia, do

not permit the import of meat or meat products from processing plants where recycled water

has been used anywhere in the plant. The export of meat products is regulated by the

Department of Agriculture and Water Resources, which uses the 2008 AQIS Meat Notice, Export

Orders and the Food Standards Australia New Zealand to assess the potential use of recycled

water in export registered meat facilities. Water recycling and reuse proposals are currently

considered on a case by case basis.

• Direct reuse of water for irrigation is possible with minimal treatment as nutrients and salt levels

were often found to be within acceptable limits (AGWR, 2006). However, information on loading

rates and impact on local conditions both require consideration to prevent environmental

impacts.

When not recycled within the plant’s operations, treated wastewater effluents are normally

discharged into sewer and/or external water bodies. The minimum requirements for the discharge

into sewer and surface water are summarized in Table 8 (ANZECC, 2000; Hamawand, 2015). BOD

concentrations into surface water should be lower than 6 mg/L which equates to BOD removal of

99.9% for an initial feed concentration of 4,000 mg BOD/L. A substantial source of contamination is

addition of surfactants as a result of the cleaning process. The limit for anionic detergent is set at 0.5

mg/L for drinking water and up to 1.0 mg/L for other purposes water (Hamawand, 2015).

Table 8. Guidelines for wastewater disposal into sewer and surface waters.

Disposal method Pollutant concentration limit (mg/L)

TSS BOD COD TN FOG

Sewer 1,000-1,500 300-3,000 3 x BOD - 50-200

Surface water 10-15 5-10 3 x BOD 0.1-15 2-15

5.2 Milestone 2. An integrated microalgae cultivation system for the red meat

processing industry

In this project we propose the integration of microalgae cultivation with the treatment of the

wastewaters generated in abattoirs as represented in Figure 1. Anaerobic and aerobic treatments are

commonly used in abattoirs to reduce the organic and nutrient levels in the abattoir wastewaters.

However, some major limitations exist for both treatments. Although anaerobic treatments

efficiently remove organic matters whilst producing biogas, nutrient removal is not effectively

performed and high nitrogen and phosphorus concentrations are found in AD effluents. Similarly, a

large range of nutrients concentration measured in AD piggery effluents is reported in the literature:

values range from 1,198 to 3,630 mg/L and from 100 to 600 mg/L for ammonia and phosphorus,

respectively (Ayre, 2013). Aerobic treatments are well known for efficiently removing organic matter

as well as nutrients; however, their high energy requirement makes these methods expensive. Most

importantly, aerobic treatments target nutrient removal other than nutrient recovery, thus not

considering potential recovery of valuable resources.

The use of microalgae for the removal of organic contaminants and nutrients from wastewaters is

referred to as phycoremediation (Benemann et al., 1977; Cuellar-Bermudez et al., 2017). Microalgae

comprise a large group of autotrophic microorganisms with cells composed of proteins,

carbohydrates, lipids, fatty acids, pigments, vitamins, and enzymes that can have value for human

use (Cuellar-Bermudez et al., 2017). Extensive research started to flourish in the eighties and more so

in the last decade as microalgal culture growth has shown great potential in applications not only

limited to wastewater treatment and nutrient reduction, but also to produce biofuel, food

supplements, protein-rich animal feed, fertilizer for crops and pharmaceutical products (Oswald,

2003). Coupling the treatment of wastewater with the cultivation of microalgae is seen a win–win

strategy for both pollution control and biofuel production (Craggs et al., 2013; Zhang et al., 2016):

the wastewater represents a continuous and abundant source of water and nutrients needed for

algal growth, whilst algae cultivation improves the treatment of wastewater by removing organic

pollutants and reducing nutrient concentration. An extensive review on microalgae cultivation recent

advances and its integration with slaughterhouse wastewaters is summarized in Appendix 9.2.

As a large producer of wastewater, the food industry has investigated the applicability of microalgae

cultivation systems to enhance wastewater treatment. There are two typical applications of

microalgae cultivation systems that have been mostly applied to treat piggery wastewaters:

• The microalgae cultivation process is used as a substitute of secondary biological treatments

(e.g., aerobic and anaerobic processes). The substrate used to grow microalgae is the primarily

treated wastewater effluent which is high in organics and nutrients. The algae biomass is mostly

used to produce biofuel, e.g., biodiesel or bioethanol (Fallowfield and Garrett, 1985; Zhu et al.,

2013; Maroneze et al., 2014).

• The microalgae cultivation process is applied on the AD effluent which is depleted in organics

but still high in nutrients. The algal biomass is recycled back to the AD process to enhance

methane production or used for by-products, e.g., biofuel and animal feed. The integration of

the AD process and microalgae cultivation have shown to improve discharge effluent quality and

methane yield (Hernández et al., 2013; Molinuevo-Salces et al., 2016).

The most relevant studies on the treatment of piggeries and abattoir wastewaters by microalgae

cultivation systems are summarized in Appendix 9.2, Tables A2.1 and A2.2. The integration of

microalgae cultivation and AD processes has received increasing interest as it offers an economically

and technologically attractive solution to the management and post-treatment of AD effluents,

normally very high in both nitrogen and phosphorous concentrations (Cai et al., 2013). The Algae

R&D Centre at Murdoch University has strong capability in the application of microalgae cultivation

systems to AD effluents (Ayre, 2013; Borowtizka and Moheimani, 2013; Nwoba et al., 2016). The

work by Ayre (2013) suggests the use of the harvested biomass as either food source to enhance pig

production or as a biomass to enrich the AD process. Alternatively, algae biomass can also be used as

a crop fertilizer. The harvest of microalgae on AD effluents has been shown as a positive impact on

the operation costs and environmental footprint of Australian piggeries (Ayre, 2003).

5.3 Milestone 3. Alternative water sources identification and wastewater quality

assessment

The objective of Milestone 3 is to characterize the wastewater streams generated at the reviewed

Australian abattoirs, assess them based on their suitability to be integrated with a microalgae

cultivation process, and propose a reconfiguration of the current wastewater treatment flowsheets.

The full analysis is reported in Appendix 9.3.

Theory and experimental works on phycoremediation techniques have shown that an adequate

substrate for microalgae to grow needs to be low in organics (e.g., COD, BOD, FOG) and high in

nitrogen and phosphorus content. In general, the optimal wastewater stream to be integrated with a

microalgae cultivation process is the AD effluent which is characterized by a low organic and high

nutrient content. The low concentrations of sugar and organics found in AD effluents minimize the

presence of bacteria and selectively favor the growth of microalgae species. Extensive research

conducted at Murdoch University and the study by Wang et al. (2016) suggest the use of undiluted

anaerobically treated effluents as optimal candidates for microalgae growth. The experimental work

of Maroneze et al. (2014), Taskan (2016) and Hernandez et al. (2016) have shown successful growth

of microalgae on primarily treated abattoir wastewaters (i.e., high in organic content); however, the

suitability of such substrates needs to be validated by ad-hoc, long-term experimental tests.

Based on the characterization of the wastewater streams and the most recent experimental work on

abattoir wastewater and microalgae harvesting (Maroneze et al., 2014; Hernandez et al., 2016), two

alternative scenarios are identified at Site G:

• Scenario A: The effluent from the anaerobic pond is used as substrate for microalgae growth

system, thus bypassing the current aerobic treatment process and reducing the size of further

storage downstream. The low concentration of FOG and BOD (8 ± 5 mg/L and 54 ± 54 mg/L for

FOG and BOD, respectively) and high nutrient content (151 ± 42 mg/L and 26 ± 7 mg/L for TN

and TP respectively) are within literature values and suitable for microalgae cultivation system.

• Scenario B: The primarily treated wastewater effluent is used as a substrate for microalgae

cultivation, thus substituting the current biological treatment (i.e., anaerobic and aerobic) with

microalgae. The concentration of FOG and COD (179 ± 219 mg/L and 1,328 ± 2,080 mg/L for FOG

and COD, respectively) might limit the growth of microalgae on the primarily treated

wastewater effluent, although literature studies suggest microalgae could grow well on similar

substrates.

The characterization of the wastewater streams at Sites A, C and D has shown that a relatively low

concentration of organics and high content of nutrients are found in streams generated from the

wash down of cattle and kill floor. Combining these two wastewaters leads to a resulting stream

(COD from 2,000 to 3,400 mg/L; FOG from 70 to 320 mg/L; TKN from 150 to 700 mg/L; TP from 18 to

25 mg/L) that could potentially be used as substrate for microalgae growth, in accordance with the

experimental conditions tested in recent literature studies (Maroneze et al., 2014; Hernandez et al.,

2016). However, the reconfiguration of the current flowsheets for the cattle wash down and kill floor

streams to by-pass AD and go straight to microalgae cultivation would cause considerable changes in

the current operations without a significant improvement of the final stream composition ahead of

the microalgae process (refer to Appendix 9.3 for detailed calculations). For this reason, at Sites A

and D, it is recommended to limit the application of the microalgae cultivation system on the AD

effluent only. However, if a new wastewater treatment process has to be designed for an abattoir,

by-passing AD and going straight to microalgae cultivation might be a cost-effective option for some

wastewater streams generated within the abattoir’s operations. In this configuration, blending of all

streams prior microalgae as well as treating each stream in a dedicated microalgae cultivation system

(i.e., with an algae culture specific for each wastewater streams) are two options that are worth

assessing.

Similarly, given the current process flowsheet, the AD effluent generated at Site G provides the

optimal solution for integration with the microalgae cultivation process. The low strength

wastewater generated at Site G seems particularly suitable for a microalgae cultivation process as

the concentration of organics and nutrients in the post AD stream is well within the range for

microalgae growth.

Based on the assumptions on water quality and flowrate data and on the process flowsheet currently

implemented at the reviewed abattoirs (refer to Appendices 9.1 and 9.3 for details), the AD effluent

has been identified as the most suitable stream for integration with a microalgae cultivation system.

The AD effluent compositions at Sites A, D and G are summarized in Table 9.

Table 9. Wastewater streams selected for integration with the microalgae cultivation system. NA: not available data. Italics highlighted values are estimated based on literature data and

assumptions made by the authors.

Site A Site D Site G

Wastewater stream AD effluent AD effluent AD effluent

Volume (kL/d) 2,423 2,150 1,750

TCOD (mg/L) 700 1,100 54 ± 54 as BOD

TS (mg/L) NA NA NA

FOG (mg/L) 257 136 8 ± 5

TKN (mg/L) 245 254 151 ± 42 as TN

NH4-N (mg/L) 239 229 NA

TKP (mg/L) 38 34 26 ± 7 as TP

PO4-P (mg/L) 33 32 NA

5.4 Milestone 4. Algae-cultivation system design

5.4.1 Microalgae cultivation approach

Algal cultivation systems have evolved in different technologies. The two most common cultivation

system designs are known as open ponds and closed photobioreactors (Borowtizka and Moheimani,

2013); the first being commonly used for large-scale commercial production in favorable climatic

conditions (Craggs et al., 1997; Raes et al., 2014). Although originally used only to hold wastes, open

ponds were observed to reduce pollution such as organic matter and nutrient concentrations by

allowing the growth of bacteria and microalgae (Benemann et al., 1977). Since then, they have been

used as the main technology to harvest microalgae for treatment of municipal, industrial and

agricultural wastewaters (Oswald, 2003). The most accepted open pond cultivation systems are

paddlewheel driven raceway ponds which are currently utilized in large scale commercial

applications due to their low capital expenditure and simple operation. Open raceway ponds are

shallow ponds (i.e., normally between 15 to 25 cm deep), equipped with a paddle wheel mixing

mechanism to keep the microalgae suspended in the water. They use atmospheric CO2 (with some

additional CO2) to reach high biomass productivity. Biomass concentrations of up to 1 g/L dry weight

and productivities of 60-100 mg/L/d dry weight have been reported in commercial applications

(Mohemiani, 2005). The algal biomass produced and harvested from these systems can be converted

through various pathways to biofuels, for example recycling to AD for biogas production,

transesterification of lipids to biodiesel, fermentation of carbohydrate to bioethanol and high

temperature conversion to bio-crude oil (Park et al., 2011). A large footprint, potential contamination

by unwanted algal species and other organisms, and challenging control of operating parameters

(e.g., temperature, light) are the main disadvantages of open raceway ponds (Raes et al., 2014;

Nwoba et al., 2016; Chaudry et al., 2017). Evaporation losses and a low microalgal biomass (e.g., 0.5

g/L) induced by poor mixing and low light penetration are also some potential limitations (Chaudry et

al., 2017).

Closed photobioreactors (PBRs) are an alternative microalgae cultivation system. Closed PBRs are

made up of transparent material which can pass light. The major operational difference between

open ponds and closed PBRs is related to the number of biotic and abiotic factors that can be

regulated to optimize and stimulate growth, thus leading to high productivity in closed PBRs. Other

distinct advantages of PBRs over raceway ponds are the absence of evaporation and reduction of

contamination by unwanted species. Big bag system, flat plate (vertical or inclined) and tubular

(serpentine type or Biocoil) reactors are different types of closed PBRs. The main disadvantage of the

use of closed PBR is the very high capital and operational costs (Moheimani, 2005) which makes its

selection less favorable for commercial applications and has limited their applicability on a large

scale. Amongst typical limitation of the process itself, closed PBRs require a cooling system, which

increases operational costs, and have shown a greater oxygen build-up, which reduces productivity

(Raes et al., 2014).

Both open ponds and closed PBRs have been tested at experimental scale in microalgae cultivation

experiments on pre and post AD abattoirs wastewaters (Hernandez et al., 2016; Taskan, 2016).

Although biomass productivity is normally higher in PBRs, similar ammonium removal rate has been

found in open ponds and PBRs (Nwoba et al., 2016). This result could be a consequence of the fact

that removal of ammonia in open ponds is not only biological (e.g., uptake by microalgae) but also

due to stripping in open atmosphere. Due to their commercial maturity, simplicity of operations,

longer durability, lower capital and operational costs comparing to PBRs (Mohemiani, 2005),

paddlewheel driven open raceway ponds are the technology of choice for the cultivation of

microalgae in this study.

Several microalgae have been reported as good candidates for wastewater bioremediation including

Chlamydomonas sp., Euglena sp., Micractinium sp., Botryococcus sp., Coelastrum sp., Chlorella sp.,

Scenedesmus sp., Oscillatoria sp. and Spirulina sp. (Nwoba et al., 2016). It is now common practice to

favor the cultivation of a microalgae consortium over monocultures because of simplicity of

operations and also because single microalgal strains find it difficult to remove all the nutrients

simultaneously from wastewaters. Chlorella and Scenedesmus have shown to be highly robust and

versatile due to their tolerance to different wastewater conditions. Ayre et al. (2017) and Nwoba et

al. (2016) reported Chlorella sp., Scenedesmus sp. and a pennate diatom can grow efficiently on

undiluted AD piggery effluents with up to 1,600 mg/L NH4-N, although previous investigations have

found high ammonia concentrations toxic to microalgae (high NH4+ concentrations at pH higher than

8 shift the chemical equilibrium towards NH3 which is considered toxic for algae). Similar results on

the growth of Chlorella sp. on undiluted piggery slurry have been found by Wang et al. (2016).

In our study, the choice of which microalgal species to harvest will be determined by the suitability of

the identified strain to grow on abattoir wastewaters and by the final use of the cultivated algal

biomass. Chlorella and Scenedesmus sp. are found suitable as a source of animal feed or biogas by

direct recycle to the AD lagoon (Nwoba et al., 2016). Species of Botryococcus have shown a high oil

content (up to 75% by weight), which can be extracted and then converted/upgraded to high quality

liquid biofuel (Chaudry et al., 2017). Due to its well-known dynamics, Chlorella sp. is used in this

project as the microalgae of reference. Modelling assumptions concerning algae productivity,

methane production and market value, are based on literature and experimental values of Chlorella

growth.

5.4.2 Mass and energy balances at selected abattoirs

The results of the mass and energy balances calculated at Sites D and G are presented below. Note

that all the models consider the AD effluent as the optimal substrate for microalgae cultivation (Table

9).

Site D – Mass and energy balances

The results of the mass balance of the microalgae cultivation system on the AD effluent at Site D are

shown in Figure 5. For the calculation of the carbon dioxide available for algae growth, the methane

production potential of the pre AD stream has been considered equal to 9,783 m3/d (Jensen and

Batstone, 2013). A Redfield ratio C:N:P = 196.5:15.8:1 is calculated, which makes nitrogen the

nutrient limiting the growth of microalgae. Based on the stoichiometric reaction (Eq. 1) and the

concentration of nutrients in the AD effluent, a theoretical algae biomass production of 5,221 kg/d is

calculated (Figure 5). As nitrogen is the limiting nutrient, its percentage of removal from the water

stream is 100%. About 99% of the incoming phosphorous is expected to be consumed daily by algae

growth.

Recent studies conducted at Murdoch University have demonstrated the suitability of Chlorella sp. to

grow on wastewaters characterized by very high ammonia and turbidity, thus further demonstrating

the ability of this microalga to grow on challenging substrates. Borowitzka (1992), Lundquist et al.

(2010) and Collet et al. (2011) consider an annual average productivity of Chlorella equal to 25

g/m2/d (Table 1). At a pond depth of 30 cm (Table 1), a total area of open raceway pond equal to 21

ha is needed to grow the estimated 5,221 kg of algae biomass per day (Figure 5). A significant

amount of water, equal to 856 kL, is expected to evaporate daily, thus an equivalent volume of water

is needed to be added to maintain the concentration ratio of nutrients and biomass.

At full scale operations, the microalgae cultivation system is expected to operate at steady state, thus

the harvesting rate equates the rate at which algae biomass grows (i.e., 5,221 kg/d). Assuming a

concentration of algae in the ponds equal to 0.5 g/L (Collet et al., 2011) and an efficiency of

harvesting and dewatering equal to 90% (Collet et al., 2011), a flow rate of 11,603 kL is harvested

daily from the ponds (Figure 5). After cultivation and harvesting, dewatering of algae is required to

remove water from the algae biomass. In current commercial microalgae production plants,

harvesting and dewatering represents a significant part of the overall production costs (Chaudry et

al., 2017). Microalgae dewatering methods can be performed in two stages. Primary dewatering

(thickening) is done by settling and flocculation, achieving a 20-fold concentration factor and a 1%

solids biomass. Secondary dewatering includes further filtration and centrifugation and allows

achieving concentration of biomass up to 30% solids. At this concentration, the microalgae product

can be used for a variety of applications, such as extraction of oil and pharmaceutical products, on-

site animal feed and fertilizer. Further dewatering by heating and drying allows reaching as high as

90% solids concentration of biomass, which is required whether transportation of the algae biomass

products for off-site uses is necessary. The obtained dry biomass can be used very efficiently for

many applications, such as recycle to animal feed, oil extraction and biofuel production, as well as

being transported at lower costs. At a 90% efficiency of the dewatering process and a final 30% solids

biomass stream, the algae biomass grown at Site D and output of the cultivation and dewatering

systems achieves a concentration of 300 g/L and a mass of 5,221 kg/d at a flow rate of 17 kL/d

(Figure 5).

Together with a dewatered microalgae biomass product, the other output of the system is a stream

of water that is depleted in nutrients (Figure 5). Part of the clean water product is used within the

microalgae process to make up for evaporation losses (Figure 5), and the remaining clean water

(1,276 kL/d, Figure 5) can be recycled back to the abattoir or discharged. Further filtration and

treatment to remove the remaining algae biomass in the nutrient-depleted water stream might be

necessary before recycle.

The daily energy demand of each system’s process is highlighted in Figure 5 and summarized in Table

10. Unit energy consumption rates refer to literature values summarized in Table 1. A daily and

annual energy demand of 3.5 MWh and 1.2 GWh, respectively, has been estimated for the treatment

of the AD effluent by microalgae cultivation at Site D (Table 10). For a 21 ha system, the energy

consumption relative to pond mixing by a paddlewheel mechanism is equal to 28% of the overall

energy consumption and 16 MWh/ha/y, which sits at the lower end of the 19 to 28 MWh/ha/y range

given for open pond cultivation in Australia (Campbell et al., 2011). The dewatering system achieving

a 30% solids output by centrifugation represents 41% of the total daily energy consumption (Table

10).

Table 10. Energy consumption of the microalgae cultivation system at Site D. Wastewater stream sent to microalgae cultivation: AD effluent.

Energy demand kWh/day % of total

Paddlewheel mixing 1,002 28.3

Harvesting and dewatering 1,450 40.9

Water pumping 687 19.4

CO2 pumping 403 11.4

Total energy demand 3,543 100

Figure 5. Mass balance and system sizing of the microalgae cultivation system at Site D. Wastewater stream sent to microalgae cultivation: AD effluent.

Site G – Mass and energy balances

The results of the mass and energy balance calculations of the microalgae cultivation system on the

post AD effluent at Site G are summarized in Figure 6 and Table 11. The introduction of a microalgae

cultivation step on the AD effluent implies the substitution of the current aerobic treatment with the

microalgae process (Appendix 9.3, Figure A3.1).

A theoretical algae biomass production of 2,802 kg/d is calculated at Site G (Figure 6). Nitrogen is

found to be the nutrient limiting growth (C:N:P = 239.17:12.84:1), thus the resulting water stream is

expected to be 100% depleted in nitrogen. The efficiency of removal of phosphorous is calculated at

80% and a final concentration of TP in the water is estimated at 1.4 mg/L. Note that the nitrogen and

phosphorous concentrations in the AD effluent are measured by Site G personnel as total nitrogen

and phosphorous, and measurements of ammonia and phosphate are not available. Although it is

realistic to assume the majority of post AD nitrogen and phosphorous is in the form of ammonia and

phosphate, this assumption will need to be validated with a more detailed characterization of the

post AD stream. At Site G, the methane generated in the anaerobic pond is not currently being

captured. Communication with Site G personnel advised that capturing the methane is amongst the

abattoir’s short-term priorities. In the mass balance calculations, it is assumed that a methane

production potential of 4.5 m3 CH4 per kL of wastewater is produced by anaerobically digested

slaughterhouse wastewaters (Jensen and Batstone, 2012 and 2013), thus producing 7,875 m3 CH4/d.

Considering combustion of one mole of methane produces one mole of CO2 (Eq. 2), enough carbon

dioxide will be generated daily for the estimated algae biomass of 2,802 kg/d.

At an algae productivity value of 25 g/m2/d and a pond depth of 30 cm, a total area of open raceway

pond equal to 11 ha is needed to grow the estimated mass of algae per day. Considering the same

harvesting and dewatering system used for Site D is also applicable on Site G, the final microalgae

product is a stream with a concentration of biomass equal to 300 g/L and a daily flow rate of 9 kL

(Figure 6). The resulting nutrient-depleted clean water stream has a total volume of 1,281 kL/d

(Figure 6).

A daily and annual energy demand of about 1.8 MWh and 604 MWh, respectively, has been

estimated for the treatment of the AD effluent by microalgae cultivation at Site G (Table 11 and

Figure 6).

Table 11. Energy consumption of the microalgae cultivation system at Site G. Wastewater stream sent to microalgae cultivation: AD effluent.

Energy demand kWh/day % of total

Paddlewheel mixing 538 29.4

Harvesting and dewatering 778 42.5

Water pumping 398 21.8

CO2 pumping 116 6.3

Total energy demand 1,830 100

Figure 6. Mass balance and system sizing of the microalgae cultivation system at Site G. Wastewater stream sent to microalgae cultivation: AD effluent.

5.4.3 Mass and energy balances of the anaerobic digestion of algae biomass

The variety of uses associated with algae biomass makes it a very versatile product for abattoirs as it

can be used to both produce additional revenue by selling algae products (e.g., animal feed and

fertilizer) and/or offset some of the environmental impacts generated from the wastewater

treatment, such as its energy demand and GHG emissions. Site D abattoir has been used as the

reference site to integrate the mass and energy balances developed in Figure 5 with an AD step on

the cultivated algae biomass. The objective is to assess the feasibility of producing biogas, i.e.,

electricity, from algae whilst minimizing the re-dissolution of nutrients in the final clean water

product. The methodology developed by Collet et al. (2011) and the experimental results on AD of

Chlorella vulgaris found by Ras et al. (2011) are used to model the process at Site D. The results of

this modelling exercise quantify the energy demand (as the identified most important environmental

impact) of the integrated AD-microalgae cultivation system where the whole, or a fraction of, algae

biomass is used to produce electricity as methane biogas.

As discussed earlier, the products of microalgae cultivation are a nutrient-depleted effluent that can

be discharged and/or recycled, and an algae biomass stream concentrated at 30% solids. The main

environmental impact associated with this process is the energy demand of 3.5 MWh/day (also equal

to 2.5 MJ/kg of cultivated algae), required mainly for pond mixing and algae dewatering (Table 10).

The estimated energy demand is at the high range of the LCA studies reviewed by Handler et al.

(2012), who determined an energy requirement associated with the cultivation and dewatering

stages ranging between 0.6 to 2 MJ/kg of algae. Our estimate at Site D is therefore quite conservative

and a lower energy demand might be found in the practice.

Amongst the identified possible uses of the cultivated biomass, its use as animal feed and fertilizer

are potentially the most straightforward and beneficial for the abattoir. However, whether the

biomass is to be sold and transported off-site, further drying of the biomass to a 90% solids product

is required, thus increasing the energy demand of the overall process. The opportunity of using the

whole, or a fraction of, algae biomass through AD to produce electricity and offset 3.5 MWh/day

energy demand is also an attractive option to improve the environmental footprint of the abattoir.

The process flowsheet diagram of the integrated AD-microalgae scenario is shown in Figure 7. Note

that dewatering of algae biomass before AD only requires a 5% solids product output of

centrifugation, thus energy savings of the cultivation-dewatering process are expected in the

integrated AD-microalgae process. The degradation of the microalgae biomass during AD is a mature

process that is expected to produce enough electricity to offset the 3.5 MWh/day energy demand.

However, at an HRT long enough to promote maximum methane production, a nearly complete

mineralization of nitrogen and phosphorous occurs, thus causing the release of nutrients in the liquid

digestate (i.e., liquid stream output from AD, Figure 7). Even if the liquid digestate is blended with

the nutrient-depleted water recycled from the algae dewatering step, the concentration of nutrients

might reach too high values for recycling and disposal. Nutrient mineralization by AD can be

controlled by keeping the HRT of the AD process short; however, short HRTs would generate less

methane, thus less electricity. In order to analyze the tradeoff between methane production and

nutrient mineralization at Site D, some scenarios of the integrated AD-microalgae cultivation process

are modelled hereafter. The amount of generated electricity and the nutrient concentration in the

blended water (liquid digestate plus nutrient-depleted water, Figure 7) are quantified as a function of

the fraction of algae biomass sent to AD and the HRT of the AD process. The performances of the AD

of the microalgae Chlorella at HRTs of 16, 28 and 46 days are derived from Collet et al. (2011) and Ras

et al. (2011) and summarized in Table 12. The results of the different modelled scenarios are

presented in Table 13.

Figure 7. Schematic process flowsheet diagram of the integrated AD-microalgae cultivation system.

Table 12. Anaerobic digestion performances of microalgae Chlorella at different hydraulic retention times (HRT) of the AD process. Experimental data derived from Collet et al. (2011) and

Ras et al. (2011).

Parameters Value

HRT of anaerobic digestion (days) 16 28 46

Methane fraction in biogas (%) 30 50 70

Methane conversion (mLCH4/gVSS) 147 240 292

Nutrient mineralization (%) 19 68 90

COD removal (biodegradability of carbon fraction) (%) 33 51 56

VSS fraction (gVSS/gTSS) 0.9 0.9 0.9

COD fraction (gCOD/gVSS) 1.37 1.37 1.37

Lower heating value of biogas (kWh/m3) 3a 6.11a 6.11a a Value of 6.11 kWh/m3 (22 MJ/m3) derived by Banks presentation (online at: http://www.valorgas.soton.ac.uk/Pub_docs/JyU%20SS%202011/CB%204.pdf). The value of 3 kWh/m3 at 30% CH4 biogas is estimated by the authors.

Table 13. Results of modelled anaerobic digestion of algae biomass produced daily at Site D as a function of the HRT and the biomass fraction sent to AD.

Scenario

1 Scenario

2 Scenario

3 Scenario

4 Scenario

5 Scenario

6

AD operating conditions

HRT (days) 46 46 46 28 28 16

Fraction of biomass to AD (%) 100 15 50 100 50 100

AD Input

Flow rate (kL/d) 104 16 52 104 52 104

Algae biomass (kg/d) 5,221 783 2,611 5,221 2,611 5,221

Algae biomass (g/L) 50 50 50 50 50 50

AD Output

Biogas (m3/d) a 1,379 207 689 1,587 793 937

Energy generation (kWh/d) b 9,994 1,499 4,997 8,215 4,107 2,911

Energy demand (kWh/d) 3,415 2,472 2,860 3,478 2,892 3,282

Energy offset (%) c 293 61 175 236 142 89

N in blended water (mg/L) d 344 55 179 260 135 73

P in blended water (mg/L) d 47 8 25 36 19 10 a Net amount of biogas after internal recycle to AD for heat supply

b Based on the conversion of biogas to electricity as given in Collet et al. (2011) and equal to 9.94 kWh/m3 of biogas

c Percentage calculated as the energy produced by AD of algae biomass in each scenario divided by total energy demand

d Concentration of nutrients in the final blended water for recycle/discharge resulting from blending liquid digestate with nutrient-depleted water

In order to offset the energy demand of the integrated AD-microalgae cultivation system and

produce excess electricity, more than half of the entire biomass needs to be anaerobically digested at

an HRT long enough to promote full methanisation (longer than 28 days, Scenario 1, 3, 4 and 5, Table

13). This process, however, causes the re-dissolution of 60 to 80% of the nutrients in the liquid

digestate, leading to their concentration in the blended water equal, or even higher, than those

measured in the abattoir secondarily treated wastewater. In order to limit the mineralization of

nutrients to levels that would allow the final blended water to be recycled or discharged (about 40

mg/L for N and 12 mg/L for P, Table A4.1), either a small fraction of biomass at long HRT (15% only,

Scenario 2, Table 13) or the whole biomass at a short HRT (16 days, Scenario 6, Table 13) are to be

treated through AD. In both cases the amount of produced electricity is enough to offset more than

half of the AD-microalgae system energy demand (61% and 89% for Scenario 2 and 6, respectively,

Table 13), whilst keeping the concentration of nutrients in the blended effluent within acceptable

levels (about 55-70 mg/L for N and 8-10 mg/L for P, Table 13).

Amongst the modelled scenarios, Scenario 6 seems to be the most appropriate. The short HRT limits

the re-dissolution of nutrients to a concentration in the final blended water that is adequate for

recycling, whilst generating about 90% of the energy demand of the AD-microalgae cultivation

system. The solid digestate and remaining post AD algae biomass is still high in protein content, thus

making it a suitable source of animal feed. The mass and energy balances of the integrated AD-

microalgae process modelled in Scenario 6 are summarized in Figure 8 for Site D and in Figure 9 for

Site G.

Figure 8. Mass and energy balances of the integrated AD - microalgae cultivation system at Site D.

Figure 9. Mass and energy balances of the integrated AD - microalgae cultivation system at Site G.

5.5 Milestone 5. Environmental impact analysis

The full environmental impact analysis developed in Milestone 5 is reported in Appendix 9.4. A

summary of the main results is given below.

The results of the qualitative environmental impact and risk assessment identify several positive

environmental impacts of the proposed microalgae cultivation system, as opposed to the negative

environmental footprint of current practices. The conventional treatment and management of AD

wastewater effluents currently implemented in abattoirs most often include the use of a small

fraction of the treated effluent for irrigation, with the majority of it stored indefinitely in evaporation

ponds. Such practice leads to mostly negative environmental impacts related to:

• Generation of large volumes of water with high nutrient concentrations, thus not suitable for

on-site recycle, except for irrigation;

• Possible greenhouse gas emissions due to storage in open ponds of large volumes of water with

elevated content of ammonia nitrogen;

• Potential eutrophication of soils and surface waters, nutrient imbalance, pest and disease in

plants due to the high content of nitrogen and phosphorous in the water used for irrigation;

• Potential nitrogen contamination to groundwater;

• Inefficient use of large areas of land dedicated to evaporation and storage ponds;

• Loss of the environmental and economic value of the treated wastewater effluent associated

with potential resource recovery of water, nitrogen and phosphorus.

Further treatment to reduce nutrient concentrations by appropriate technologies is the main

preventative measure to minimize the identified environmental impacts and risks.

Positive and negative environmental impacts have been identified when a microalgae cultivation

process is integrated in the treatment flowsheet. The main negative environmental impact is related

to the on-site recycle of the wastewater effluent and is identified as the potential contamination of

the potable water used for meat processing operations. Preventative measures to reduce this risk to

acceptable levels are required, such as different reticulation systems for potable and recycled water,

proper personnel training and limited permitted on-site uses of recycled water. Another negative

environmental impact relates to the large land footprint dedicated to microalgae cultivation in

raceway ponds; however, this is also a drawback of open ponds storage and other suggested cost-

effective technologies for nutrient removal (e.g., wetlands). Several positive environmental impacts

of growing microalgae on the AD effluents have been identified:

• Reclamation of the environmental and economic value of the wastewater effluent in terms of

water and nutrient recovery;

• Generation of large volumes of water that are suitable for recycling on-site and off-sit or safe to

discharge to surface water bodies;

• Generation of an algae biomass product that is suitable for re-use with the abattoir’s operations

or for sale to available markets;

• Sequestration of carbon dioxide currently generated by the conventional wastewater treatment

process (e.g., AD) and fixation into algae biomass.

5.6 Milestone 6. Cost benefit and uncertainty analysis

5.6.1 Cost benefit analysis of the proposed microalgae cultivation system

The estimate of capital and operational costs of the microalgae cultivation system is summarized in

Table 14 for Site D and Site G, for both scenarios with and without AD. Total CAPEX and annual OPEX

are reported separately and the contribution of each cost element is shown in Figure 10. Note that

the same cost estimates per hectare have been used for Site G and D (refer to Table 2, Section 4.5),

therefore the contribution of each cost element shown in Figure 10 is the same for Site G and D. As

an indicative estimate, the annual expenditures of CAPEX and OPEX are calculated for the case where

all of the capital cost is sourced from a bank loan. In this case a 10-year lifetime project is assumed

with an annual interest of 6.35% (Wijihastuti, 2017). Costs are also given per unit area and per unit of

cultivated algae biomass (Table 14). Estimates below are all expressed in Australian dollars.

A total CAPEX of M$ 3.9 and 2 are calculated for Site D and G respectively (Table 14), half of which is

due to the construction of raceway ponds and the necessary infrastructures (buildings, roads, water

pumping and electrical system, Figure 10a). OPEX costs amount to M$ 2.1 and 1.3 per year (Table

14). The largest contribution to OPEX is represented by the costs associated with maintenance,

insurance and taxes on the capital infrastructures (Figure 10b). Decreasing initial capital is therefore

going to significantly decrease the annual operational costs as well. It should be noted that the costs

associated with labour (about 20% of the total OPEX, Figure 10b) are likely to be overestimated as

they refer to a newly built and stand-alone wastewater treatment plant. In the case of existing

wastewater treatment plants operating on the abattoir premises, the additional labour costs

associated with the microalgae cultivation system could be partially absorbed by the existing

personnel, thus potentially reducing the labour costs reported in Table 14. Finally, the electricity

required to mix the ponds, pump water and dewater the algae biomass up to a 30% solids product,

represents a small fraction of the total OPEX (Figure 10b).

In the case of the integrated AD-microalgae cultivation system, CAPEX costs increase from M$ 3.9

and 2 for Site D and G to M$ 5.6 and 3 for Site D and G, respectively (Table 14). The higher CAPEX is

due to the added capital associated with anaerobic digesters, gas turbines to burn methane and

digestate centrifugation (Figure 10c). Although the electricity costs are almost reduced to zero

(Figure 10d) and the labour costs are equivalent to the scenario without AD, OPEX costs are higher

due to the maintenance, insurance and tax related costs associated with a higher CAPEX. The total

annual expenditures and the unit production costs of algae are also higher in the case where AD on

the grown biomass is integrated to the process (Table 14 and Figure 11).

Given its higher CAPEX, OPEX and unit costs of production, the integrated AD-microalgae cultivation

system does not seem to represent the best option for Sites G and D. Moreover, careful operations

of the AD of the algae biomass to ensure minimal nutrient re-dissolution in the blended water (Figure

8 and 9) make the process increasingly complex. On the contrary, the simplicity and lower costs

associated with the use of the algae biomass product as on-site fertiliser and animal feed make the

scenario without AD an attractive option for abattoir operations. Moreover, the nutrient-depleted

water can be directly recycled on-site or safely discharged to surface water bodies.

Table 14. Summary of CAPEX and OPEX estimate for Site D and G abattoirs.

Microalgae cultivation system

Integrated AD - Microalgae cultivation system

Unit Site D Site G Site D Site G

Capital Costs

Open raceway pond – clay lined AU$ 1,036,299 556,194 1,036,299 556,194

Buildings, roads, drainage, vehicles AU$ 140,098 75,192 140,098 75,192

Electrical AU$ 577,410 309,903 577,410 309,903

Water piping AU$ 425,460 228,349 425,460 228,349

CO2 (flue gas+ distribution) AU$ 180,517 96,885 180,517 96,885

Dewatering system AU$ 368,631 197,848 368,631 197,848

Digesters AU$ 0 0 665,541 357,204

Biogas turbine AU$ 0 0 741,516 397,980

Inoculum system AU$ 334,081 179,305 334,081 179,305

Engineering fees AU$ 459,374 246,551 670,433 359,829

Contingency AU$ 153,125 82,184 223,478 119,943

Working capital AU$ 183,750 98,621 268,173 143,932

Total CAPEX AU$ 3,858,742 2,071,032 5,631,633 3,022,563

Operational costs

Electricity AU$/year 315,675 163,085 33,081 11,413

Labour - Plant Manager AU$/year 113,520 113,520 113,520 113,520

Labour - Engineer AU$/year 84,480 84,480 84,480 84,480

Labour - Lab Analyst AU$/year 63,360 63,360 63,360 63,360

Labour - Administration AU$/year 60,720 60,720 60,720 60,720

Labour - Technician/Pond Operator AU$/year 100,320 50,160 100,320 50,160

Maintenance/ Insurance AU$/year 385,874 207,103 563,163 302,256

Tax AU$/year 1,010,623 542,413 1,474,952 791,624

Total OPEX AU$/year 2,134,572 1,284,841 2,493,596 1,477,534

Annual instalment for a 10 years loan at 1.3% inflation rate and 6.35% bank interest

Annual CAPEX AU$/year 533,008 286,071 777,897 417,506

Annual OPEX AU$/year 2,134,572 1,284,841 2,493,596 1,477,534

Total annual expenditures AU$/year 2,667,580 1,570,913 3,271,493 1,895,040

Costs per unit area

Pond area ha 21 11 21 11

Total CAPEX AU$/ha 184,763 184,763 269,652 269,652

Total OPEX AU$/year/ha 102,207 114,625 119,398 131,815

Total annual expenditures AU$/year/ha 127,728 140,146 156,645 169,062

Costs per unit production of algae biomass

Total annual biomass ton/year 1,723 925 1,723 925

Unit cost production of algae AU$/kg 1.55 1.70 1.90 2.05

Figure 10. The contribution of different cost elements to the total CAPEX (a, c) and OPEX (b, d) for the microalgae cultivation system without (a, b) and with (c, d) anaerobic digestion. Capital cost elements: Pond = raceway pond; Infr = buildings, roads, etc; Elec = electrical layout; Wat = water

piping; CO2 = flue gas distribution system; Dewat = dewatering system; Dig = digesters; Biog = biogas trubines; Inoc = inoculum; Eng = engineering fees; Cont = contingency fees; WorkCap =

working capital.

Figure 11. a) Total annual expenditures and b) unit production costs for Sites D and G.

5.6.2 Sensitivity and uncertainty analysis

The results of the mass and energy balances and the cost-benefit analysis have demonstrated the

microalgae cultivation system without AD of the grown biomass as the most suitable, simple to

operate and cost-effective option for the reviewed abattoirs. A sensitivity analysis of the

mathematical model and economic analysis developed on Site G and D is performed to evaluate

process uncertainties and modelling assumptions. The mathematical model and economic analysis as

reported in Figure 5 and 6 and Table 14 constitute the base case of the following sensitivity analysis.

The modelling parameters tested by the sensitivity analysis are summarized in Table 3 of the

Methodology Section.

The sensitivity of process variables i) daily algae production (kg/d), ii) pond area (ha), iii) nutrient-

depleted water for recycle (kL/d), iv) total CAPEX ($), v) total OPEX ($/year), and vi) algae production

cost ($/kg) at each varying modelling assumption is represented as a percentage variation from the

base case. As an example, the percentage variation from its base case value of the total CAPEX due to

a +25% variation of algae productivity is calculated by Eq. 6. A positive percentage variation indicates

an increase in CAPEX costs due to the +25% increase in algae productivity. Likewise, a negative

percentage variation indicates capital costs decrease with increasing productivity. It should be noted

that when one modelling parameter is varied, the others are kept constant and equal to their base

case value. For example, when sensitivity analysis is performed on algae productivity, all the other

parameters (e.g., nitrogen content in the wastewater, flow rate, pond construction costs, etc.) are

equal to their base case values. Note that the energy costs associated with pond mixing and

dewatering have only been varied between -25% to +25% from the base case as the cost analysis has

shown a relatively low contribution of power costs to the overall capital and operational costs. A very

low impact of pond mixing and dewatering energy consumption on the process variables have been

found, thus results associated with these modelling parameters are not discussed further.

(%)%25

VariationPercentageCAPEXCAPEX

CAPEXCAPEX

typroductivicasebase

typroductivicasebasetyproductivi

Eq. 6

The results of the sensitivity analysis on Site D are summarized in Figure 12. Out of the nine

modelling assumptions tested in the sensitivity analysis, the daily algae productivity per unit pond

area (expressed as mass of algae grown per m2 per day) is the most influential parameter. Although it

doesn’t influence the mass of algae grown daily (which is calculated based on stoichiometric and

Redfield Ratio, Section 2, Eq. 1), the algae productivity significantly impacts on pond size, which in

turn impacts on the amount of nutrient-depleted water effluent (through evaporation) and on

capital, operational and unit production costs (Figure 12d). A decrease of algae productivity by 50%

(equal to 13 g/m2/d) causes a 90% increase in cultivation area and capital costs, as well as a 64%

increase in OPEX and 70% increase in unit production costs. Augmented algae productivity by 50%

(equal to 38 g/m2/d) causes a 20% decrease in cultivation area and capital costs, 13% decrease in

OPEX and 15% decrease in unit production costs.

The composition of the incoming wastewater (AD effluent from the abattoir’s existing wastewater

treatment plant) in terms of its nitrogen and phosphorous content is also an important parameter as

it influences the amount of algae biomass that stoichiometrically can grow on the wastewater. By

controlling the amount of biomass grown daily, the wastewater composition influences cultivation

area, amount of final water effluent (through evaporation) and costs (Figure 12a and b). At Site D,

the molar ratio between nitrogen and phosphorus in the incoming wastewater is very close to the

Redfield stoichiometric ratio of 16:1. For this reason, an increase in N (or P) content doesn’t impact

on the system’s performance as the growth of algae would be limited by the content of P (or N).

Whether a decrease in N (or P) occurs, the maximum amount of algae that can grow daily on the

wastewater would be proportionally limited by N (or P), further causing a decrease in cultivation

area, capital and operational costs (Figure 12a and b). A net 34% and 17% increase in the amount of

final water effluent and unit production costs, respectively, occur as a consequence of a 50%

decrease in N (or P).

A directly proportional relationship has been found between the variation of wastewater flowrate

and the process variables (Figure 12c): an increase (or decrease) in the amount of wastewater sent

daily to the algae pond generates an equal increase (or decrease) in daily algae production, pond

area, nutrient-depleted water for recycle, total CAPEX and OPEX. As a ratio between costs and algae

biomass, a lower impact of variation in the wastewater flow rate has been found on the algae unit

production costs (Figure 12c). A directly proportional relationship exists between the variation of

capital costs (i.e., pond construction, dewatering system and lumped CAPEX) and costs performance

variables (i.e., capital, operational and unit production costs). A 100% increase in pond construction

(i.e., about AUD 100,000 per hectare) generates an increase in capital, operational and unit

production costs of about 34%, 22% and 24%, respectively (Figure 12e). Likewise, a 100% increase in

the construction costs associated with the dewatering system generates an increase in capital,

operational and unit production costs of about 12%, 8% and 9%, respectively (Figure 12e). Obviously,

variations of the cost parameters do not influence algae production, pond area and water effluent,

which were omitted from graphs e, f and g of Figure 12.

The results of the sensitivity analysis on Site G are similar to Site D’s ones and summarized in Figure

13. The same relationship for Site G and D is found between wastewater flow rate, energy costs and

capital cost elements with the system’s performance. The algae productivity per unit pond area is the

most influential parameter for Site G too: its 50% decrease causes a 90% increase in cultivation area

and capital costs, a 57% increase in OPEX and 64% increase in unit production costs (Figure 13d).

Augmented algae productivity by 50% causes a 34% decrease in cultivation area and capital costs,

21% decrease in OPEX and 24% decrease in unit production costs (Figure 13d). Energy costs

associated with pond mixing and dewatering systems don’t impact on overall costs, whilst a directly

proportional relationship has been found between the variation of wastewater flowrate and capital

costs with the main performance variables (Figure 13).

Similar to Site D, the stoichiometric ratio between N and P in the incoming wastewater is the main

parameter controlling the amount of algae biomass that can grow on the wastewater (Figure 13a and

b). At a P content less than its base case value, the growth of algae is limited and controlled by

phosphorous which causes a decreasing trend in daily production, cultivation area, capital and

operational costs (Figure 13b). When nitrogen in the wastewater increases by 25 to 50%,

phosphorous becomes the nutrient responsible of controlling the daily amount of algae production,

which in turn impacts on land area and system costs (Figure 13a).

The overall variability of the selected process variables (i.e., daily algae production, pond area,

nutrient-depleted water for recycle, total CAPEX, total OPEX and algae unit production cost)

associated with the uncertainty of the modelling assumptions is summarized in Table 15. Within a -

50% to +100% uncertainty associated with the modelling assumptions, the capital costs at Site D are

characterized by an average and standard deviation of M$ 3.9 ± 1.1, with a maximum value of M$ 7.4

associated with an algae productivity as low as 13 g/m2/d. Site G CAPEX have an average and

standard deviation of M$ 2.1 ± 0.6, with a maximum value of M$ 4. OPEX ranges as M$ 2.1 ± 0.4 at

Site D and M$ 1.3 ± 0.2 at Site G.

Figure 12. Sensitivity analysis on Site D. Percentage of variation of some process variables relative to the sensitivity of a) nitrogen content in the wastewater, b) phosphorous content in the wastewater, c) wastewater flow rate, d) algae productivity per unit area, e) raceway pond construction costs, f) dewatering system construction costs, g) other capital costs. Process

variables are: Mass = daily grown algae biomass; Area = size of raceway ponds; Eff = nutrient-depleted water effluent; CAPEX = capital costs; OPEX =operational costs; UC = algae unit

production costs.

Figure 13. Sensitivity analysis on Site G. Percentage of variation of some process variables relative to the sensitivity of a) nitrogen content in the wastewater, b) phosphorous content in the wastewater, c) wastewater flow rate, d) algae productivity per unit area, e) raceway pond construction costs, f) dewatering system construction costs, g) other capital costs. Process

variables are: Mass = daily grown algae biomass; Area = size of raceway ponds; Eff = nutrient-depleted water effluent; CAPEX = capital costs; OPEX =operational costs; UC = algae unit

production costs.

Table 15. Summary of sensitivity analysis results – overall variability of major process variables.

Base case ± standard

deviation Minimum Maximum

Site D

Daily algae production (kg/d) 5,221 ± 933 2,611 7,832

Pond area (ha) 21 ± 5 10 40

Final water effluent (kL/d) 1,276 ± 249 486 1,914

CAPEX (M AUD) 3.9 ± 1.1 1.9 7.4

OPEX (M AUD) 2.1 ± 0.4 1.3 3.5

Unit costs (AUD/ kg of algae) 1.55 ± 0.24 1.15 2.63

Site G

Daily algae production (kg/d) 2,802 ± 502 1,401 4,203

Pond area (ha) 11 ± 3 6 22

Final water effluent (kL/d) 1,281 ± 164 641 1,922

CAPEX (M AUD) 2.1 ± 0.6 1.0 4.0

OPEX (M AUD) 1.3 ± 0.2 0.8 2.0

Unit costs (AUD/ kg of algae) 1.70 ± 0.25 1.3 2.8

6.0 DISCUSSION

The current project is structured into two main parts addressing a variety of deliverables. The first

part is based on an extensive review of:

• The red meat processing industry and its current wastewater practice;

• Regulation standards relative to on-site water reuse and recycle;

• Data collection and analysis of wastewater operations at several Australian abattoirs;

• Integration of microalgae cultivation methods for wastewater treatment;

• Identification of wastewater streams generated at the reviewed abattoirs that are suitable for

integration with a microalgae cultivation system.

Once specific abattoirs and wastewater streams have been selected, the techno-economic analysis of

the proposed integrated microalgae cultivation system is performed as:

• Development of mass and energy balances of the integrated microalgae cultivation system for

each selected abattoir;

• Environmental impact and risk assessment following potential on-site recycle of treated

wastewater;

• Economic analysis of the proposed system;

• Sensitivity and uncertainty analysis of the developed techno-economic model.

The following discussion is mostly focused on the outcomes of the techno-economic analysis

calculated at two abattoirs, i.e., Site D and Site G, as the most suitable abattoirs due to their

comprehensive available set of data and the suitability of the wastewater effluent currently treated

on site by anaerobic digestion to be integrated with a microalgae cultivation system. The outcomes

and discussion relative to the literature review and data collection are addressed in Sections 5.1 to

5.3 and Appendices 9.1 to 9.3.

The mass balances on Site D and G (Figure 5 and 6) estimate the mass of algae biomass produced

daily at 30% solids by the microalgae cultivation and dewatering system. The value associated with

the microalgae product depends on its final use which, in turn, is to be determined by on-site needs

(e.g., fertilizer, animal feed, biogas production) and the local market for algal products (e.g., oil

extraction and biodiesel production, off-site animal feed). The environmental and process benefits

associated with the recycle of the biomass to the AD process include augmented production of

methane, which improves the economic and energy footprint of the abattoir and reduces its

greenhouse gases emissions. Similarly, the use of biomass as on-site animal feed and/or fertilizer

improves the overall environmental and economic footprint of the abattoir. Mass and energy

balances have been developed at Sites D and G for the case where the microalgae biomass is used in

an anaerobic digestion process to produce biogas. Although the amount of energy generated by AD

of algae biomass offsets the energy demand of the integrated AD-microalgae cultivation process,

increased capital and operational costs as well as increased process complexity and nutrient

concentration in the final water effluent suggest the process without AD of the algae biomass is the

preferred option for the reviewed abattoirs.

From an energy perspective, the typical energy consumption of an abattoir is reported in two MLA

environmental performance review reports at 3,000 MJ/tHSCW (Ridoutt et al., 2015; URS, 2005) and

500 MJ/head (URS, 2005). It should be noted the range found in the literature for energy

consumption expressed per animal head is very wide, and a value between 500 and 900 MJ/head is

expected for abattoirs processing large animals. Site D processes an average of 1,100 heads (cattle

and veal) per day (Jensen and Batstone, 2013) whilst about 500 heads are processed at Site G on a

daily basis. Considering an average energy consumption of 500 MJ/head, an energy consumption of

550 GJ/d and 250 GJ/d is calculated at Site D and G, respectively (equivalent to about 152 MWh/d

and 69 MWh/d for Site D and G, respectively). The daily energy consumption of the microalgae

system estimated at Site D is 3.5 MWh/d (Table 10), which represents only 2.3% of the total daily

energy consumption of the abattoir. Similarly for Site G, the daily energy consumption of the

microalgae system is about 2.6% of the total energy demand of the abattoir.

The recommended system, its capital and operational costs together with the variability of the main

process variables as a result of the sensitivity analysis is summarized in Figures 14 and 15 for Site D

and Site G, respectively. A nutrient-depleted wastewater effluent of about 1,300 kL/d generated at

both Sites D and G is a high-value process output. Subjected to water recycling guidelines

implemented at each abattoir, the nutrient-depleted wastewater effluent can be recycled within the

abattoir operations for all the permitted uses (e.g., cleaning of yards, infrastructures and trucks,

washing of animals other than final wash, animal drinking water, fire control, irrigation of gardens

and green areas) or discharged off-site for irrigation of crops and pasture or to surface water bodies.

It should be noted that the primary objective of integrating a microalgae cultivation step in the

wastewater treatment process currently operating at abattoirs is to reduce the environmental

impacts associated with high nitrogen and phosphorus concentrations in the treated wastewater

effluents currently generated in abattoirs and stored in open ponds. In this project it was

demonstrated that a microalgae cultivation system treating the AD effluent is a very promising

technology to achieve such objective. The production of a nutrient-depleted water stream that can

be recycled within the abattoir operations and/or safely discharged to the environment is the main

end-product of the suggested process. The potential recycle of a nutrient-depleted water stream

within the abattoir’s operations reduces the need of fresh water, optimizes the water balance of the

entire facility and improves the self-sustainability and environmental footprint of the abattoir in

regard to its water use.

The grown algae biomass represents a process by-product whose intrinsic value can be exploited as a

way to offset some treatment costs and possibly produce a revenue stream. The final use of the

concentrated microalgae biomass has to be evaluated on a case-by-case basis depending on the

location and needs of the abattoir, local market for algae products, costs of handling and

transportation of the biomass. Amongst its possible uses, on-site uses such as fertilizer for crop

irrigation and use as animal feed are technically feasible and cost effective options. Off-site uses such

as sale as animal feed, pharmaceutical products and biofuel generation could also be possible

depending on the local market and the grown algal strain, although further drying of the biomass to

achieve a 90% solids product might be necessary. The use of microalgae biomass (in particular

Chlorella species) as crops fertilizer has shown to lead to positive effects on the environment in terms

of the health of soils and plants. Similarly, the use of microalgae as animal feed has shown great

potential in recent studies (Benemann, 2013), with Chlorella being one of the most robust and

versatile species in the market. The use of algae biomass as protein supplement in animal feed has

been widely suggested and researched as a sustainable way to help address the global energy, food

and environmental crisis and the current competition for resources (e.g., land and water) between

animal feed and human food supply (Benemann, 2013; Lum et al., 2013; Bleakley and Hayes, 2017).

Recent estimates indicate that 30% of the global algal production is used by the animal feed industry

and, although their nutritional profiles vary considerably with the species used, a large majority is

characterized by protein, carbohydrate, and lipid contents that are comparable, if not superior, to

conventional feeds (Lum et al., 2013). Recent estimates of the market value of Chlorella range from

AUD 5 to AUD 20 per kg of algae, with the maximum of AUD 20 being associated with a 90% dry final

product (Benemann, 2013). Considering the estimated algae production unit cost at Site D and Site G

is about AUD 1.5-1.7 ± 0.25 per kg of grown algae (base case value ± standard deviation based on

sensitivity analysis), there is a promising opportunity for the red meat processing industry to make

the microalgae cultivation system extremely cost-effective and generate potential revenue by selling

the grown biomass product as animal feed.

Figure 14. Summary of the microalgae cultivation system proposed at Site D.

Figure 15. Summary of the microalgae cultivation system proposed at Site G.

7.0 CONCLUSIONS/RECOMMENDATIONS

Overarching objective of this project is to investigate a new technological approach for the

transformation of nutrient contents in red meat processing wastewater streams into protein rich

biomass via microalgae cultivation. To address this objective, a techno-economic feasibility study of

an integrated microalgae cultivation process for treating abattoir wastewaters and for water

recycling has been developed. A thorough literature review has demonstrated the maturity and

robustness of microalgae cultivation as a cost-effective treatment technology able to capture

nutrient and harvest algae biomass whilst producing a nutrient-depleted water effluent. Through the

development of a mathematical model, the output of a microalgae cultivation system integrated on

the AD effluents currently generated at two Australian abattoirs has been quantified. The main

outcomes of the modelling exercise are summarized as follow:

• A microalgae cultivation system that receives 2,000 kL/d of AD effluent at an average

concentration of nitrogen and phosphorous ranging as 150-250 mg/L and 25-35 mg/L,

respectively, is expected to generate about 1,300 kL/d of nutrient-depleted water suitable for

recycle/discharge and about 3 to 5 tons of algae biomass product at 30% solids;

• A 80% to 100% nutrient removal from the AD effluent and fixation of about 6 to 10 tons/d of

carbon dioxide into algae biomass are quantified;

• The cost-benefit analysis has estimated a range of capital and operational costs of M$ 2-4 and

M$ 1-2, respectively, for an open raceway pond algae cultivation system followed by settling

and centrifugation for algae harvesting and dewatering;

• Algae unit production costs are expected to range within $ 1.5 to 2 per kg of algae product.

Subjected to water recycling guidelines implemented at each abattoir, the nutrient-depleted water

stream can be recycled within the abattoir operations thus improving the environmental impact of

the abattoir and reducing costs associated with purchase of freshwater. Suggested uses of the

effluent from microalgae cultivation refer to cleaning of yards, infrastructures and trucks, washing of

animals other than final wash, animal drinking water, fire control, irrigation of gardens and green

areas, irrigation of crops and pasture for fodder production. If recycle is not viable, the clean water

stream is likely to meet the guidelines for safe discharge into the sewer or surface waters. The grown

algae biomass represents a process by-product whose intrinsic value can be exploited to offset some

treatment costs and possibly produce a revenue stream. On-site as fertilizer and animal feed are

technically feasible and cost effective options.

The integrated microalgae cultivation system mitigates, and possibly removes, the environmental

impacts associated with contamination of soils, water and groundwater, and to greenhouse gas

emissions into the air. More importantly, it gives value to the wastewater effluent by recovering the

nutrients and water and ultimately improving the environmental footprint of the abattoir. Several

positive impacts of the microalgae cultivation process integrated on the AD effluent are identified:

• Reclamation of the environmental and economic value of the wastewater effluent in terms of

water and nutrient recovery;

• Recycle of large volumes of water for on-site and off-site uses;

• Generation of an algae biomass product that is suitable for on-site reuse, energy generation or

for sale to available markets;

• Sequestration of carbon dioxide currently generated by AD reactors during the current

wastewater treatment process and fixation into algae biomass.

The promising outcomes of this technology assessment pave the road for further and more detailed

explorations that aim at improving technical understanding, environmental and economic footprint

and potential for full-scale applications. Experimental test works on microalgae cultivation on

abattoir wastewaters are deemed essential to corroborate, improve and expand the techno-

economic assessment developed in this project. Recommendations for future R&D projects include

bioprospecting studies through a pilot plant implemented at the premises of an operating Australian

abattoir. Through long-term outdoor experiments, microalgae species suitable for treating abattoir

wastewaters are identified, together with the most suitable cultivation and harvesting methods,

impacts of seasonal variations of inflow streams and nutrient supplies on algae growth rates. The

optimization of microalgae growth conditions for maximum nutrient removal and the evaluation of

different microalgae sources for animal/aquaculture feed or high value products is also an expected

outcome of a bioprospecting study. Due to the high importance of algae productivity per pond

square meter and AD effluent composition (flow rate, nitrogen and phosphorous content), it is

recommended to carefully address the impacts of such parameters through ad-hoc lab and pilot

experimental test work.

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9.0 APPENDICES

9.1 Appendix 1. Reviewed Australian abattoirs

The following data on flowsheet and wastewater streams composition is sourced by two AMPC/MLA

reports produced by Jensen and Batstone in 2012 and 2013. The authors interviewed and gathered

data on wastewater source, composition, collection and treatment at six different Australian red

meat processing facilities, hereafter referred to as Sites A to F. Extensive water quality monitoring

and mass balances allowed the characterization of each wastewater stream, to eventually identify

the most critical waste streams and recommend a proper treatment process. The level of detail of

the collected data varies for each site, and the same information might not be available for all sites,

thus leading to potential inconsistencies in the data reporting. As suggested by Jensen and Batstone

(2013), Sites A, C and D provide the most accurate and comprehensive dataset, whilst the structure

of the waste handling process at Sites B, E and F prevented the collection of data from some

individual processing areas, thus the analysis of nutrient and organic loads is not as reliable as for

Sites A, C and D.

The collection of data from another beef abattoir has started as part of the current project. The

Australian beef abattoir is referred hereafter as Site G and communication between Murdoch

University and Site G is considered strictly confidential. Although not as comprehensive as for Sites A,

C and D, the information collected from Site G is used as a reference case study for the current

project together with the sites analyzed by Jensen and Batstone (2012 and 2013). Site G is a large

export-registered cattle meat processor, with a current throughput of 130,000 heads per annum and

about 2,500 heads per week. About 70% of the meat produced at Site G is for export markets in Asia,

Middle East and U.S., with the remaining 30% for domestic use supply.

9.1.1 Processing Site A

A flowsheet of wastewater sources, handling and treatment at Site A is shown in Figure A1.1. The

composition of each wastewater stream is presented in Table A1.1. Data are based on beast weight

of 600 kg. Raw data can be found in the original report by Jensen and Batstone (2012). The combined

wastewater effluent is treated in an anaerobic pond. Streams generated by slaughtering, paunch

processing, tripe and cattle wash undergo screening for solid separation prior to anaerobic digestion

(AD). Wastewater streams generated by rendering and boning activities are treated by screening as

well as saveall/dissolved air flotation (DAF) for further solid separation and collection of fat, oil and

grease. The effluent from the DAF unit is sent to AD.

Figure A1.1. Flowsheet of wastewater sources, handling and treatment at Site A (adapted from Jensen and Batstone, 2012). SP: sample point.

Table A1.1. Characterization of wastewater streams at Site A. SP: sample point (refer to Figure A1.1).

Site A

ID Stream Volume (kL/d)

TCOD (mg/L)

SCOD (mg/L)

TS (mg/L)

FOG (mg/L)

TKN (mg/L)

NH4-N (mg/L)

TKP (mg/L)

PO4-P (mg/L)

SP 1 Cattle wash 882 3,194 380 3,000 4 89 47 13 6

SP 2 Paunch liquid 311 23,908 2,064 15,800 2,603 517 36 211 160

SP 3 Paunch, tripe, green wash

330 32,707 2,170 24,800 3,883 281 15 155 101

SP 4 Kill floor 450 3,756 1,278 3,500 206 2,021 17 28 17

SP 5 Tripe wash 54 30,890 1,210 19,900 11,638 282 9 81 43

SP 7 New Render 192 40,003 7,840 24,600 5,538 1,718 41 120 73

SP 8 Total effluent cold 1,512 16,378 1,798 10,600 3,063 234 67 77 75

SP 9 Total effluent hot 911 7,209 1,600 4,800 1,138 264 44 28 17

Total effluent 2,423 12,893 1,722 8,396 2,332 245 58 58 53

9.1.2 Processing Site B

Site B is a mixed 50% beef and 50% sheep abattoir and data are based on weekly HSCW (hot

standard carcass weight). Figure A1.2 shows the flowsheet highlighting source, collection and

primary treatments of each wastewater stream at Site B. Jensen and Batstone (2012) could not

separate all the streams at Site B, therefore some streams have combined beef and sheep data. The

stream composition is shown in Table A1.2. Raw data can be found in the original report by Jensen

and Batstone (2012).

Two process trains characterize the wastewater system at Site B. A combined red stream includes

rendering, offal processing and boning, while cattle wash and sheep paunch and intestinal wash form

a second stream. Both streams go through a solid separation phase, and are then combined in a

Gross Fat Separator. The fat scarped from the top is sent to rendering, whilst the liquid is sent to a

clarifier and a DAF unit for further separation of solids and fats. No biological treatments seem to

occur at Site B (Figure A1.2), despite the high concentration of contaminants still present in the final

total effluent (Table A1.2). No further details on the wastewater treatment processes are provided

by Jensen and Batstone (2012).

Figure A1.2. Flowsheet of wastewater sources, handling and treatment at Site B (adapted from Jensen and Batstone, 2012). SP: sample point.

Table A1.2. Characterization of wastewater streams at Site B. SP: sample point (refer to Figure A1.2).

Site B

ID Stream Volume (kL/d)

TCOD (mg/L)

SCOD (mg/L)

TS (mg/L)

FOG (mg/L)

TKN (mg/L)

NH4-N (mg/L)

TKP (mg/L)

PO4-P (mg/L)

SP 1 Cattle wash 252 3,089 534 3,450 4 220 131 40 20

SP 2 Paunch liquid 421 10,777 2,280 8,100 47 377 190 233 162

SP 3 Sheep paunch 60 52,663 4,890 55,410 226 1,685 181 1,805 922

SP 4 Sheep intestinal wash

120 5,285 1,900 4,550 30 125 103 35 30

SP 5 Cattle paunch N/A 39,158 2,805 47,880 120 1,390 58 640 251

SP 6 Bone squeeze 285 44,773 - 33,200 25 4,745 131 11 34

SP 7 Buffer tank 400 13,877 2,124 16,900 29 674 197 314 149

SP 8 Saveall out 2,138 10,367 2,200 7,000 1,313 304 71 49 33

SP 9 DAF effluent 3,153 9,587 1,970 4,300 783 232 93 50 38

Total effluent 3,153 9,587 1,970 4,300 783 232 93 50 38

9.1.3 Processing Site C

A flowsheet of wastewater sources, handling and treatment at Site C is shown in Figure A1.3. The

composition of each wastewater stream is presented in Table A1.3. Each wastewater stream

generated at each operation at Site C is collected in a mixed pit prior to AD. Solid screening occurs

before the mixing with different screening processes for the cattle wash waters and the

slaughtering/rendering produced wastewaters. Data in Table A1.3 are based on beast weight of 600

kg. Raw data can be found in the original report by Jensen and Batstone (2012).

Figure A1.3. Flowsheet of wastewater sources, handling and treatment at Site C (adapted from Jensen and Batstone, 2012). SP: sample point.

Table A1.3. Characterization of wastewater streams at Site C. SP: sample point (refer to Figure A1.3).

Site C

ID Stream Volume (kL/d)

TCOD (mg/L)

SCOD (mg/L)

TS (mg/L)

FOG (mg/L)

TKN (mg/L)

NH4-N (mg/L)

TKP (mg/L)

PO4-P (mg/L)

SP 1 Cattle wash 240 1,632 680 2,250 < 1 175 82 26 14

SP 2 Paunch 200 15,028 2,096 13,370 210 506 46 256 112

SP 3 Green pit 440 5,768 774 5,350 217 276 43 96 41

SP 4 Kill room floor 108 19,257 7,380 7,290 28 3,040 41 57 20

SP 5 Screws to Rendering 21 24,490 9,900 19,240 1,717 3,050 252 417 145

SP 6 Tripe wash 432 10,392 428 2,870 687 51 6 24 13

SP 7 Rendering belt wash 25 6,903 692 4,850 3,430 164 1 19 8

SP 8 Stick water 315 22,103 2,400 13,070 6,017 718 21 108 51

SP 9 Boning room 90 - - 340 < 1 - - - -

SP 10 Red pit 949 9,683 1,324 6,190 4,400 258 10 24 14

SP 11 Cattle yards, clean overflow

171 - - 190 - - - - -

SP 12 Total effluent 2,115 10,785 893 7,530 3,350 260 62 30 15

9.1.4 Processing Site D

Site D is situated in New South Wales, Australia, and has the capability to process 12,500 bovines per

week. The abattoir has two separate processing floors one for beef and one for veal meat. The

animals are grass/grain fed and the abattoir consumes 2.5-3 ML of clean water daily. Figure A1.4

shows the flowsheet of source, collection and primary treatments of each wastewater stream at Site

D. Table A1.4 gives the composition of each stream analyzed by Jensen and Batstone (2013). Where

available, composite samples were collected, otherwise an average composition of the available

samples has been considered. Raw data and additional information can be found in the original

report by Jensen and Batstone (2013).

The waste processing operations at the Site D abattoir consists of 4 main process trains (Figure A1.4):

• Combined red wastewater includes all wastewater from the rendering plant, beef slaughter

floor, offal processing and the veal slaughter floor. The rendering plant includes several

wastewater sources including raw material bins, stick waters, boiler condensate. The beef

slaughter floor and offal processing have been collected as a combined stream. The combined

red wastewater is passed through a screen to remove course solids (recycled to rendering) and

sent to a DAF system with no polymer addition to recover fatty solids for recycling. The

remaining red wastewater flows directly to the final effluent mixing pit and is discharged to the

anaerobic lagoon.

• Paunch handling consists of paunch, foreign objects (e.g. intestinal plugs/clamps) and wash

down water/transfer water. The combined paunch stream passes through a course screen and a

screw press to remove coarse solids that are sent to composting. The remaining wastewater

flows directly to the final effluent mixing pit and is discharged to the anaerobic lagoon.

• Cattle yards’ wastewaters consist of spray water used to wash cattle before processing, bovine

urine and manure, and wash down from cleaning operations in the cattle yards. A portion of

water used in the cattle yards is recycled from the defrost collection pit. The preliminary

treatment consists in a pass through an auger screw to remove coarse solids that are sent to

composting. The remaining wastewater flows directly to the final effluent mixing pit and is

discharged to the anaerobic lagoon.

• Boning room and chillers wastewaters are collected in the defrost collection pit. This

wastewater is recycled to the cattle yards and is not directly discharged to the anaerobic lagoon.

Figure A1.4. Flowsheet of wastewater sources, handling and treatment at Site D (adapted from Jensen and Batstone, 2013). SP: sample point.

9.1.5 Processing Site E

Site E is a beef only facility situated in Queensland, Australia. Site E processes grass fed, grain fed and

organic beef, and has a capability of approximately 3,000 bovines per week. Site E consumes 1.5 ML

of clean water daily. Figure A1.5 summarizes Site E flowsheet. The composition of each wastewater

stream is presented in Table A1.5. Where available, composite samples were collected, otherwise an

average composition of the available samples has been considered. Site E includes a red wastewater

stream that combines streams from the slaughter floor, rendering plant and boning room. Site E also

has a combined green wastewater stream generated from paunch handling, offal and cattle yards.

The treatment at Site E is composed of preliminary screening and a DAF system to remove solids and

FOG. Jensen and Batstone (2013) identified some issues happening in the plant during their site visit.

Cattle wash was not operating during the sample period, thus the characterization of wastewater

coming from the cattle yards is not representative of standard operations. Site E transports cattle

hides to a fleshing shed using a water slide system, thus resulting in an additional wastewater stream

that is added to the combined red wastewater. Slaughter floor and boning room wastewater

contribute to the combined red flow, but these streams were not accessible during the sample trip,

thus no data have been measured.

Table A1.4. Characterization of wastewater streams at Site D. SP: sample point (refer to Figure A1.4).

Site D

ID Stream Volume (kL/d)

Temp

(C)

TCOD (mg/L)

SCOD (mg/L)

TS (mg/L)

VS (mg/L)

TSS (mg/L)

FOG (mg/L)

25 Paunch - pre screen 200 33 12,190 920 15,123 12,897 N/A 142

4 Paunch - post screen 200 34 5,420 850 6,946 4,753 4,370 194

24 Paunch - solids 18 m3 N/A 147,170 N/A 249,383 236,614 N/A 1,095

21 Cattle wash - pre auger 400 21 11,070 400 9,828 7,940 N/A 82

22 Cattle wash - post auger 400 19 1,800 250 1,979 1,361 1,200 10

23 Cattle wash - solids 2 m3 N/A 89,530 N/A 155,983 136,101 N/A 380

10 Combined bins 304 46 44,140 15,820 30,548 26,376 17,730 9,297

11 Combined stick 94 39 73,420 980 33,530 32,130 32,030 21,075

12 Veal room 480 31 14,120 2,270 9,335 8,942 276 < 4

9 Kill floor/offal 722 37 2,210 1,220 2,630 2,245 2,020 325

7 Combined red - pre screen 1,600 38 9,950 1,910 8,489 7,827 5,820 3,751

6 SaveAll in 1,600 36 12,790 2,790 9,264 7,830 5,620 3,300

3 SaveAll out 1,600 36 8,020 3,010 4,031 3,439 2,930 978

2 Total out 2,150 31 12,460 2,220 7,401 6,828 6,600 1,240

Site D

ID Stream TKN

(mg/L) NH4-N (mg/L)

TKP (mg/L)

PO4-P (mg/L)

25 Paunch - pre screen 266 18 167 99

4 Paunch - post screen 243 13 146 88

24 Paunch - solids 776 N/A 243 N/A

21 Cattle wash - pre auger 356 86 65 29

22 Cattle wash - post auger 129 87 18 9

23 Cattle wash - solids 1,922 N/A 475 N/A

10 Combined bins 2,076 180 164 89

11 Combined stick 492 215 114 34

12 Veal room 294 26 4 15

9 Slaughter floor/offal 154 5 20 3

7 Combined red - pre screen 353 38 39 16

6 SaveAll in 420 27 41 19

3 SaveAll out 402 38 41 33

2 Total out 438 38 56 27

Figure A1.5. Flowsheet of wastewater sources, handling and treatment at Site E (adapted from Jensen and Batstone, 2013). SP: sample point.

9.1.6 Processing Site F

Site F is a small, family owned, Australian livestock processing facility situated in North Queensland.

Site F processes cattle, veal, pigs and goats. Processing volumes and species vary through a typical

week. Figure A1.6 and Table A1.6 show the flowsheet and wastewater characterization at Site F. As a

very small processing facility, the waste and wastewater handling operations at Site F did not follow

the same structure observed at other sites. In particular:

• Blood streams do not pass through the rendering plant.

• Paunch solids and blood streams do not pass through the wastewater treatment train and are

handled using direct land application.

• Rendering wastewater is treated using a DAF designed to remove solids and recover FOG. This

primary treatment is done on the rendering effluent only.

Table A1.5. Characterization of wastewater streams at Site E. SP: sample point (refer to Figure A1.5).

Site E

ID Stream Volume (kL/d)

Temp

(C)

TCOD (mg/L)

SCOD (mg/L)

TS (mg/L)

VS (mg/L)

FOG (mg/L)

TKN (mg/L)

NH4-N (mg/L)

TP (mg/L)

PO4-P (mg/L)

1 Total effluent

962 45 10,925 1,195 6,118 4,920 1,569 272 25 47 32

2 DAF in 953 46 12,214 1,247 6,678 5,745 2,380 292 22 42 32

4 Paunch liquid

104 33 11,788 778 8,152 6,081 900 319 56 108 44

5 Red post screen

953 49 9,823 1,548 5,380 4,569 1,985 248 10 24 21

7 Stick water

17 45 80,275 7,365 40,730 37,398 17,350 1,315 74 184 47

8 Blood decanter

64 48 32,918 14,148 22,101 15,451 300 2,777 26 87 47

9 Hide 179 28 2,193 1,500 1,916 1,280 20 166 2 5 11

10 Spill 1 28

49 388 181 684 352 24 15 0 1 0

11 Spill 2 79 180,750 3,540 124,927 122,770 72,600 2,010 54 211 27

12 Fleshing shed

120 33 2,642 981 2,135 1,640 144 96 1 8 8

13 Paunch pre screen

119 28 18,596 1,140 18,366 14,901 990 333 96 142 3

14 Running room

32 38 10,613 3,342 7,324 5,896 366 485 31 72 25

Table A1.6. Characterization of wastewater streams at Site F. SP: sample point (refer to Figure A1.6).

Site F

ID Stream Volume (kL/d)

Temp (oC)

TCOD (mg/L)

SCOD (mg/L)

TS (mg/L)

VS (mg/L)

FOG (mg/L)

TKN (mg/L)

NH4-N (mg/L)

TP (mg/L)

PO4-P (mg/L)

1 Cattle wash

4 19 4,347 1,013 4,117 2,939 60 218 115 33 13

2 Total render

17 37 21,936 2,370 10,241 9,631 9,578 513 153 70 34

3 Paunch & KF after trommel

99 37 2,631 708 2,086 1,734 148 98 49 15 6

5 Total effluent

168 33 6,719 1,148 3,471 3,038 2,258 178 74 27 12

7 Paunch solids

3 29 121,030 N/A 118,765 103,036 2,094 2,790 N/A 983 N/A

8 Cattle blood

23 33 43,065 2,128 21,873 20,785 864 4,093 385 50 36

9 Pig blood 13 36 3,906 3,252 2,968 2,704 24 375 25 9 4

Figure A1.6. Flowsheet of wastewater sources, handling and treatment at Site F (adapted from Jensen and Batstone, 2012). SP: sample point.

9.1.7 Processing Site G

Site G has been approached by Murdoch personnel and agreed at providing data that can assist with

the current project. Please note that the information provided by Site G is strictly confidential and for

internal reference only. The operations at Site G include standard processes such as slaughtering and

rendering and a flowsheet of the wastewater treatment process is shown in Figure A1.7.

The fresh water entering the meat processing plant varies seasonally at 50 – 60 ML per month during

summer months, and 40 – 55 ML per month during winter. Non-potable water is supplied by the

pipeline water supply scheme. The water is then chlorinated on site prior to storage in covered and

locked tanks. The average consumption of water at Site G ranges from 2 to 5 kL per head per day.

Note that no water reuse or recycle is undertaken. The total volume of the daily produced

wastewater is unknown; however, the measuring system is going through several updates that will

provide routine measurements of flow rate across the plant. The wastewater is directed from each

process operation (i.e., slaughtering, boning and rendering, cleaning of chilling and freezing areas)

into one drainage system through to the wastewater treatment plant. Solids are screened using a

rotary wedge wire screen and sent for composting. The post-screening effluent is sent to a DAF-

saveall unit to separate the remaining solids and allow floatation of fats. Solids are collected, de-

watered and processed into compost. The effluent enters a settling pond where it is met with storm

water from drainage. Solids are periodically removed from the settling pond and processed as soil

conditioner. The primarily treated wastewater leaves the settling pond through a weir system and is

pumped through to the anaerobic pond where anaerobic digestion occurs. A small percentage of the

settling pond effluent, e.g. 10%, is added as raw feed into the aerobic pond. The effluent from the

anaerobic pond is sent to an aerobic pond for biological nitrogen removal. The pond is composed of

three sections: anoxic zone for denitrification, aerobic zone for nitrification and settling zone for

sludge recycle. After the biological treatment, four storage ponds are used for storage over periods

of high rainfall when irrigation is not required, as well as to provide further retention time for settling

of solids, natural aeration and evaporation. Two biofilter plants are used to control odors from the

rendering plant and to keep constant moisture ahead of the biological treatment. A fraction of the

treated effluent is pumped to surrounding land for irrigation of pasture and perennial crops. The

current wastewater treatment system does not incorporate phosphorous reduction; therefore, the

abattoir removes phosphorous by the use of a cropping program. Selected crops are planted that

have a high uptake of phosphorous, potassium and nitrogen then cropped and used as cattle feed.

Water and wastewater flow rates

There is only a limited amount of flow rate data available at Site G. The following information has

been provided by personal communication with Site G personnel. Estimated flow rates are calculated

based on the provided information and assumptions made by the authors.

The average consumption of water at Site G ranges from 2 to 5 kL/head/day (personal

communication, 17 November 2016) and between 2,200 and 2,800 animals are processed weekly

(personal communication, 17 November 2016). Assuming the plant operates 5 days a week, 440 to

560 animals are slaughtered every day, thus leading to a water consumption ranging from 880 to

2,800 kL/day. Our literature review has shown that similar values of fresh water consumption and

wastewater generation are found in Australian abattoirs (Section 5.1 of the current report; Ridoutt et

al., 2015). At Site G we assume that the amount of combined wastewater entering the treatment

plant is within the same range as the fresh water consumed in the slaughtering process, i.e., from

880 to 2,800 kL/day. An average value of 1,750 kL/day of generated wastewater is considered in this

project. If steady state is assumed in the operations of the wastewater treatment plant (i.e.,

wastewater coming in is the same as treated water going out on a daily basis), a flowrate equal to

1,750 kL/day is assumed throughout the wastewater treatment plant (i.e., at the monitoring stations

ID 1, 2, 3, 4 and 5, Figure A1.7). The treated wastewater is withdrawn from storage ponds 3 and 6

(Figure A1.7) and used for irrigation. Table A1.7 shows the flow rate of the treated wastewater

leaving the plant on a monthly basis from January to September 2016.

Figure A1.7. Flowsheet of the wastewater treatment plant at Site G. Water quality sampling points

are highlighted.

Table A1.7. Flow rate of treated wastewater effluent used for irrigation at Site G.

Month Flow from storage

pond 3 (kL) Flow from storage

pond 6 (kL) Total flow

(kL)

January 455 816 1,270

February 317 953 1,270

March 249 796 1,045

April 485 916 1,401

May 474 1,053 1,526

June 729 964 1,693

July 379 823 1,202

August 370 1,146 1,515

September 379 984 1,363

October NA NA NA

November NA NA NA

December NA NA NA

Water quality of wastewater streams

The quality of the wastewater is measured monthly at different sampling points distributed

throughout the treatment plant. Site G has provided water quality data measured at the seven

sampling points of Figure A1.7, at a monthly frequency and for three years (2014, 2015, 2016) for a

total of 36 measurements at each sampling point.

Table A1.8 summarizes the average and standard deviation of nutrients and organic compounds

calculated over the three-year period, from January 2014 to December 2016. Values of pH are not

reported in the table but they have also been measured as a routine monitoring variable. A constant

pH ranging from 6.6 to 6.8 has been measured at most sampling points. A lower pH (5.3 ± 1.2) is

measured at the exit of the aerobic treatments (sampling point 5, Figure A1.7). Considerable

variability with large standard deviations is found for FOG, BOD and TSS, while more consistent data

are measured for nitrogen, phosphorus and TDS. Large differences of organic content in wastewaters

are reported in the literature for different abattoirs; however, it is expected that similar

concentrations are measured in time in the same abattoir. To better understand the variability in the

data, each year has been analyzed separately, with particular attention on seasonal patterns. Tables

A1.9, A1.10 and A1.11 summarize the average and standard deviation of the data calculated for each

year separately. The year 2014 and 2015 show a large variability in FOG, TSS and BOD, whilst 2016

has more consistent measurements for BOD although large variability still exists for FOG and TSS. No

obvious seasonal patterns have been detected in any water quality variable. It should be noted that

the wastewater composition at the exit of the settling pond and at the entry of anaerobic pond

(sampling points 2 and 3, Figure A1.7) should be the same. The data and their averages as reported in

Table A1.8 are not overly different; however, some discrepancy occurs for the concentration of TDS,

TSS and BOD. The raw data shows several missing values at sampling point 2 in 2014 and 2015, due

to the water level in the pond being too low to take samples. A complete set of data is measured in

2016 and more consistent values are found at sampling point 2 and 3 during this year. In the

following analysis, it was decided to ignore sampling point 2 and use the data measured at sampling

point 3 as representative of the wastewater composition entering the AD process.

The efficiency of removal by each treatment process and by the overall wastewater treatment plant

is calculated using the average values of each compound’s concentration over the three years (Table

A1.12) and over each year separately (Table A1.13). The efficiency of removal by the overall

treatment is calculated as the difference between the compound’s concentration measured at

sampling point 1 (saveall entry, Figure A1.7) and the compound’s concentration measured at

sampling point 7 (settling pond 6 exit, Figure A1.7). The difference is then divided by the compound’s

concentration at sampling point 1 to express the removal as a percentage of the compound’s

concentration in the raw wastewater. The efficiency of removal by each treatment process is

calculated as the difference between the compound’s concentrations between two consecutive

sampling points. Negative values indicate the concentration has increased between two consecutive

sampling points. For example, negative values are expected for total nitrogen after anaerobic

digestion as ammonium nitrogen is normally released by the AD process. Note that the efficiency of

removal is calculated as a ratio of concentrations under the flow rate steady state assumption (same

inflow and outflow at each treatment step). The wastewater treatment plant at Site G achieves high

efficiencies of removal for FOG and BOD with 98% of the incoming concentration removed (Table

A1.12). FOG and BOD concentrations are mostly lowered by primary treatments (saveall unit and

settling pond) and by biological treatments. Only 37% of the nitrogen concentration entering the

wastewater treatment plant is removed, despite the aerobic pond being specifically designed for

nitrogen removal. The current wastewater treatment system does not incorporate phosphorous

reduction, as seen by the TP removal efficiencies reported in Table A1.12 and Table A1.13. The

removal of FOG and BOD has been consistent throughout the years with efficiencies higher than 95%

(Table A1.13). Both nitrogen and phosphorous removal improved largely in 2016, with 62% and 32%

of nitrogen and phosphorous removed, respectively (Table A1.13).

The water quality standards applicable to the treated wastewater effluent were given by Site G

personnel and reported in Table A1.14. The load of each compound is estimated by multiplying the

flow rates withdrawn monthly from storage ponds 3 and 6 (Table A1.7) with the compound’s

concentration measured monthly at sampling points 6 and 7 (exit of storage ponds 3 and 6, Figure

A1.7). The load of each compound is calculated for the months from January to September 2016 as

flow rate data haven’t been provided from October to December 2016. Due to the absence of

phosphorous removal, the load of total phosphorus always exceeds the guideline of 50 kg/year

(Table A1.15). The total load of nitrogen is also above the guidelines despite having aerobic

treatments operating at Site G (Table A1.15). Although the efficiency of nitrogen removal of the

aerobic pond in 2016 was significantly higher than in the other years (Table A1.13), the nitrogen load

in 2016 exceeds the limit of 300 kg/year (Table A1.15). The concentrations of FOG, BOD and TDS

measured monthly at sampling points 6 and 7 in 2016 comply with the guidelines, as they are less

than 50 mg/L for FOG and BOD and less than 1,500 mg/L for TDS. Unfortunately, no limits on

nutrients’ concentration have been communicated by Site G.

Table A1.8. Wastewater characterization at different sampling point for three years. Average and standard deviation are calculated on the complete dataset (from January 2014 to December 2016)

at each sampling point.

Sampling point ID FOG (mg/L) TN (mg/L) TP (mg/L)

Saveall entry 1 395 ± 413 123 ± 62 25 ± 14

Settling pond exit 2 157 ± 129 142 ± 50 18 ± 9

Anaerobic pond entry 3 179 ± 219 122 ± 35 19 ± 7

Aerobic entry 4 8 ± 5 151 ± 42 26 ± 7

Aerobic exit 5 5 ± 1 126 ± 37 27 ± 6

Settling pond 3 exit 6 7 ± 4 85 ± 32 24 ± 5

Settling pond 6 exit 7 7 ± 5 78 ± 30 24 ± 6

Sampling point ID TDS (mg/L) TSS (mg/L) BOD (mg/L)

Saveall entry 1 938 ± 330 1,652 ± 1,011 587 ± 440

Settling pond exit 2 760 ± 241 1,050 ± 421 430 ± 322

Anaerobic pond entry 3 658 ± 198 1,169 ± 1,049 664 ± 1,040

Aerobic entry 4 672 ± 98 530 ± 770 54 ± 54

Aerobic exit 5 757 ± 154 457 ± 933 14 ± 15

Settling pond 3 exit 6 745 ± 150 77 ± 75 12 ± 12

Settling pond 6 exit 7 755 ± 168 70 ± 64 12 ± 12

Table A1.9. Wastewater characterization in 2014 at Site G. Average and standard deviation are calculated at each sampling point.

Sampling point ID FOG (mg/L) TN (mg/L) TP (mg/L)

Saveall entry 1 494 ± 383 83 ± 32 22 ± 13

Settling pond exit 2 250 ± 108 136 ± 89 9 ± 3

Anaerobic pond entry 3 193 ± 183 118 ± 28 19 ± 4

Aerobic entry 4 11 ± 7 147 ± 33 30 ± 9

Aerobic exit 5 5 ± 0 125 ± 28 31 ± 7

Settling pond 3 exit 6 7 ± 4 82 ± 34 27 ± 5

Settling pond 6 exit 7 7 ± 7 74 ± 27 27 ± 6

Sampling point ID TDS (mg/L) TSS (mg/L) BOD (mg/L)

Saveall entry 1 754 ± 294 1,319 ± 860 630 ± 642

Settling pond exit 2 630 ± 210 920 ± 515 388 ± 372

Anaerobic pond entry 3 622 ± 91 1,018 ± 1,015 811 ± 1,520

Aerobic entry 4 663 ± 81 615 ± 962 59 ± 71

Aerobic exit 5 835 ± 161 301 ± 226 7 ± 6

Settling pond 3 exit 6 793 ± 138 121 ± 113 8 ± 9

Settling pond 6 exit 7 802 ± 127 116 ± 86 8 ± 8

Table A1.10. Wastewater characterization in 2015 at Site G. Average and standard deviation are calculated at each sampling point.

Sampling point ID FOG (mg/L) TN (mg/L) TP (mg/L)

Saveall entry 1 501 ± 530 123 ± 80 24 ± 17

Settling pond exit 2 151 ± 139 139 ± 32 21 ± 10

Anaerobic pond entry 3 202 ± 262 117 ± 36 20 ± 9

Aerobic entry 4 8 ± 5 158 ± 63 27 ± 6

Aerobic exit 5 6 ± 2 132 ± 19 25 ± 3

Settling pond 3 exit 6 8 ± 6 103 ± 31 25 ± 4

Settling pond 6 exit 7 7 ± 5 98 ± 30 25 ± 4

Sampling point ID TDS (mg/L) TSS (mg/L) BOD (mg/L)

Saveall entry 1 871 ± 322 1,838 ± 1,428 542 ± 363

Settling pond exit 2 804 ± 274 1,027 ± 362 558 ± 458

Anaerobic pond entry 3 637 ± 288 1,038 ± 876 863 ± 956

Aerobic entry 4 721 ± 84 548 ± 918 55 ± 38

Aerobic exit 5 742 ± 132 242 ± 118 25 ± 21

Settling pond 3 exit 6 785 ± 153 57 ± 25 15 ± 12

Settling pond 6 exit 7 818 ± 184 45 ± 29 13 ± 11

Table A1.11. Wastewater characterization in 2016 at Site G. Average and standard deviation are calculated at each sampling point.

Sampling point ID FOG (mg/L) TN (mg/L) TP (mg/L)

Saveall entry 1 191 ± 213 163 ± 37 30 ± 11

Settling pond exit 2 120 ± 122 146 ± 41 20 ± 8

Anaerobic pond entry 3 143 ± 215 131 ± 42 19 ± 8

Aerobic entry 4 5 ± 1 148 ± 27 23 ± 4

Aerobic exit 5 5 ± 0 122 ± 54 24 ± 5

Settling pond 3 exit 6 5 ± 0 70 ± 25 21 ± 5

Settling pond 6 exit 7 5 ± 1 62 ± 23 20 ± 5

Sampling point ID TDS (mg/L) TSS (mg/L) BOD (mg/L)

Saveall entry 1 1,189 ± 214 1,798 ± 540 586 ± 247

Settling pond exit 2 788 ± 233 1,124 ± 435 373 ± 194

Anaerobic pond entry 3 716 ± 167 1,453 ± 1,253 317 ± 141

Aerobic entry 4 636 ± 111 430 ± 380 47 ± 52

Aerobic exit 5 693 ± 144 828 ± 1,575 9 ± 6

Settling pond 3 exit 6 662 ± 132 57 ± 48 14 ± 14

Settling pond 6 exit 7 650 ± 147 50 ± 39 13 ± 16

Table A1.12. Efficiency of removal by the wastewater treatment process calculated over the three years at Site G.

Treatment process Efficiency of removal (%)

FOG TN TP TDS TSS BOD

Saveall and settling pond 55 1 23 30 29 -13

Anaerobic treatment 96 -24 -36 -2 55 92

Aerobic treatment 32 17 -1 -13 14 74

Settling pond 3 -26 33 9 1 83 12

Settling point 6 3 8 -1 -1 9 6

Overall treatment 98 37 3 20 96 98

Table A1.13. Efficiency of removal by the wastewater treatment process calculated over each year separately at Site G.

Treatment process Efficiency of removal (%)

FOG TN TP TDS TSS BOD

2014

Saveall and settling pond 61 -42 14 18 23 -29

Anaerobic treatment 95 -24 -55 -7 40 93

Aerobic treatment 51 15 -4 -26 51 88

Settling pond 3 -33 34 12 5 60 -12

Settling point 6 -5 11 -2 -1 5 -2

Overall treatment 99 11 -24 -6 91 99

2015

Saveall and settling pond 60 5 15 27 44 -59

Anaerobic treatment 96 -36 -31 -13 47 94

Aerobic treatment 28 17 5 -3 56 55

Settling pond 3 -42 22 2 -6 77 41

Settling point 6 14 5 -1 -4 20 10

Overall treatment 99 20 -5 6 98 98

2016

Saveall and settling pond 25 20 37 40 19 46

Anaerobic treatment 96 -13 -21 11 70 85

Aerobic treatment 6 18 -3 -9 -92 80

Settling pond 3 0 43 11 5 93 -55

Settling point 6 -5 11 2 2 13 7

Overall treatment 97 62 32 45 97 98

Table A1.14. Water quality standards applicable to the treated wastewater effluent at Site G.

Parameter Unit FOG BOD TN TP TDS

Load kg/year or kg/day NA < 30 kg/day < 300 kg/year < 50 kg/year NA

Concentration mg/L 50 50 NA NA 1500

Table A1.15. Load of contaminants in treated wastewater effluent discharged for irrigation from January to September 2016 at Site G.

FOG TN TP TDS TSS BOD

Settling pond 3 (kg/year) 20 237 76 2,472 208 56

Settling pond 6(kg/year) 47 540 170 5,600 292 117

Total effluent (kg/year) 66 777 245 8,072 501 173

Annual load guideline at Site G (kg/year) NA < 300 < 50 NA NA NA

9.2 Appendix 2. Review of microalgae cultivation systems

9.2.1 Microalgae cultivation systems

The use of microalgae for the removal of organic contaminants and nutrients from wastewaters is

referred to as phycoremediation (Benemann et al., 1977; Cuellar-Bermudez et al., 2017). Extensive

research started to flourish in the eighties and more so in the last decade as microalgae cultivation

systems have shown great potential in applications not only limited to wastewater treatment and

nutrient reduction, but also for the production of biofuel, food supplements and pharmaceutical

products (Oswald, 2003). In their pioneer work, Benemann et al. (1977) consider the huge potential

of microalgae harvesting not only in wastewater treatment applications but also as a source of

methane and fertilizer. Microalgae comprise a large group of autotrophic microorganisms with cells

composed of proteins, carbohydrates, lipids, fatty acids, pigments, vitamins, and enzymes that can

have value for human use (Cuellar-Bermudez et al., 2017). The production of biofuel is the most

widespread application of microalgae cultivation as several advantages over traditional energy crops

have been identified (Benemann, 2013; Cai et al., 2013). Microalgae have shown higher fuel yield

potential and lower water demand than traditional energy crops, and have the ability to store

significant amounts of energy-rich compounds which can be utilized for the production of several

distinct biofuels including biodiesel and ethanol (Abou-Shanab et al., 2013). Microalgae have shown a

rapid growth and a high oil content of 20 - 50% on a dry weight basis. Microalgae do not compete

with crops for arable land and freshwater because they can be cultivated in brackish water and on

non-arable land. Moreover, microalgae fix carbon dioxide very effectively as up to 50% of overall

biomass is comprised of carbon, thus reducing greenhouse gas emissions and improving air quality

(Cai et al., 2013). Algae biomass residue after lipid extraction can be used as a nitrogen source, such

as a protein-rich animal feed or fertilizer for crops (Oswald, 2003; Benemann, 2013). To this end, the

biochemical composition of biomass should be stable and suitable for the target use with a potential

toxicity that meets the quality standard and a suitable market to consume the output of bioproducts

(Zhang et al., 2016).

To date, the mass cultivation of algae for liquid biofuel production has been unsuccessful due to very

low cost of fossil fuels, high environmental footprint of microalgae in terms of need for land,

consumption of water and fertilizers (Park et al., 2011). A niche opportunity has been identified in

the integration of algae cultivation processes with wastewater treatment (Craggs et al., 1997; de-

Bashan et al., 2004; Park et al., 2011; Borowtizka and Moheimani, 2013; Jebali et al., 2015; Mennaa

et al., 2015). Wastewater represents a continuous and abundant source of water and nutrients for

algae biomass production, whilst algae cultivation represents an option to improve the treatment of

wastewater by removing organic pollutants and reducing nutrient concentration. Coupling the

treatment of wastewater with the cultivation of microalgae is therefore a win–win strategy for both

pollution control and biofuel production (Craggs et al., 2013; Zhang et al., 2016): the risk of

eutrophication due to effluent discharge is minimized by removing inorganic nutrients and microalgal

biomass can be used for biofuels, animal feed, and fertilizer production. Several microalgae have

been reported as good candidates for wastewater bioremediation including Chlamydomonas sp.,

Euglena sp., Micractinium sp., Botryococcus sp., Coelastrum sp., Chlorella sp., Scenedesmus sp., and

Oscillatoria sp. (Nwoba et al., 2016).

Algae cultivation systems have evolved in different technologies. The two most common cultivation

system designs are known as open ponds and closed photobioreactors (Borowtizka and Moheimani,

2013; Zittelli et al., 2013); the first being commonly used for large-scale commercial production in

favorable climatic conditions (Craggs et al., 1997; Raes et al., 2014). Although originally used only to

hold wastes, open ponds were observed to reduce pollution such as organic matter and nutrient

concentrations by allowing the growth of bacteria and microalgae (Benemann et al., 1977). Since

then, they have been used as the main technology to harvest microalgae for wastewater treatment

and pollution control (Oswald, 2003). The most accepted open pond cultivation systems are raceway

ponds which are currently utilized in large scale commercial applications due to their low capital

expenditure and simple operation. High rate algal ponds (HRAPs) are shallow, open raceway ponds

and have been used for treatment of municipal, industrial and agricultural wastewaters since their

large-scale production was proposed by Oswald and Golueke (1960). The algal biomass produced and

harvested from these wastewater treatment systems can be converted through various pathways to

biofuels, for example anaerobic digestion to biogas, transesterification of lipids to biodiesel,

fermentation of carbohydrate to bioethanol and high temperature conversion to bio-crude oil (Park

et al., 2011). The major operational differences between open ponds and closed photobioreactors

are the number of factors that can be regulated and influenced to optimize and stimulate growth. In

open systems, there is only a limited control over growth conditions (e.g., light), evaporation of

water and invasion of non-desired species (Raes et al., 2014; Nwoba et al., 2016). Closed

photobioreactors, on the other hand, are characterised by the better regulation and control of many

of the important biotic and abiotic limiting growth factors. However, closed photobioreactors also

have several disadvantages such as cooling requirement, which increases operational costs, and

greater oxygen build-up, which reduces productivity (Raes et al., 2014).

Despite the promising outcome of many experimental tests, microalgae cultivation in wastewater

still faces some scale-up challenges (Cuellar-Bermudez et al., 2017). There are many critical

environmental (light and temperature), operational (pH, CO2 and nutrients) and biological

(zooplankton grazers and algal pathogens) parameters that affect microalgae cultivation in

wastewater. In particular the complex and varying characteristics of the wastewaters, contamination

of the algal culture by unwanted bacteria and competitive species, and unstable biomass production

are the main issues that have traditionally limited the scale up of microalgal cultivation systems from

experimental to pilot scale (Cai et al., 2013). The external contamination by other heterotrophic

microorganisms is one of the main limitations of microalgae cultivation systems (Maroneze et al.,

2014). Chlorella species are easily cultivated and efficient in the removal of nutrients; however, in

large-scale applications contamination by other species has limited this species applicability (Taskan,

2016). The maintenance of a monoculture in full-scale is prohibitively expensive and technically

difficult to operate (Maroneze et al., 2014). In this sense, improving microalgae culture stability is a

challenge to be surmounted before the industrial application of microalgal heterotrophic bioreactors

in wastewater treatment facilities. Latest research has moved from mono-cultures towards mixed

microbial cultures as the latter have been shown more effective than pure cultures in biological

treatment systems. The identification of the microbial species responsible for the treatment of

pollutants is therefore important to improve treatment performance. Zhang et al. (2016) found that

wild microalgal strains isolated from the local environment are particularly suitable for open-pond

systems, especially for the cases when wastewater is used as a substrate for growth.

9.2.2 Current applications of microalgae cultivation systems in wastewater treatment

As a large producer of wastewater, the food industry has investigated the application of microalgae

cultivation systems to enhance wastewater treatment. The majority of the existing literature use

piggery wastewaters as a substrate to grow microalgae to i) improve the treatment of wastewaters

and meet discharge criteria, and ii) produce biofuel from algal biomass.

One of the first applications of microalgae treatment on pig slurry is the pilot plant scale system

tested by Fallowfield and Garrett (1985). A culture of Chlorella was used to treat piggery

wastewaters. The wastewater went through some pre-treatments to remove solids and suspended

matter in order to reduce light attenuation. A 9-time dilution was also required to further reduce

turbidity. The authors found light as a limiting factor to be considered when treating piggery

wastewaters with algae, however the removal of nutrients and organic matter was quite substantial.

Phosphorus and nitrogen removal ranged from 42 to 89% and from 54 to 98%, respectively.

BOD removal was approximately 98%.

A pilot plant was proposed and tested by Garden (2005) to improve ammoniacal-nitrogen treatment

of wastewater and harvest algal biomass for biofuel production. The author identified induced air

flotation as an appropriate algae separation technology and cultivated algae in a high-rate open

pond. The harvesting of algae was successful and nitrogen levels were kept at very low

concentrations. A colony of Micractinium sp. and Scenedesmus sp. were identified.

Zhu et al. (2013) tested an integrated approach which combined freshwater microalgae Chlorella

zofingiensis cultivation with piggery wastewater treatment for biodiesel production. Piggery

wastewaters were pre-treated by autoclave sterilization, to prevent contamination of the microalgae

culture, and diluted with distilled water to five different COD concentrations. Pollutants in piggery

wastewater were efficiently removed with COD, TN and TP removal ranging from 66% to 80%, from

69% to 83% and from 85% to 100%, respectively. The diluted piggery wastewater with an initial

concentration of COD equal to 1,900 mg/L provided an optimal nutrient concentration for C.

zofingiensis cultivation, thus resulting in the highest nutrient removal and productivities of biomass,

lipid and biodiesel.

Six different microalgal cultures were cultivated in an experimental study by Abou-Shanab et al.

(2013). The study aimed at improving wastewater treatment by reducing nutrient concentrations and

producing biodiesel. Piggery wastewater effluents, that were biologically-treated by an

anaerobic/oxic process, were used as a substrate for algal growth. The highest removal of nitrogen

(62%), phosphorus (28%), and inorganic carbon (29%) was achieved by Chlamydomonas Mexicana, a

microalgae belonging to Chlorophytes phyla. The authors suggest that C. mexicana is one of the most

promising candidates for simultaneous nutrient removal and high-efficient biodiesel production.

To improve the cost-effective production of energy from algae cultivation systems, one promising

application is the use of microalgae biomass in anaerobic digestion processes for the production of

methane. Anaerobic digestion (AD) is a mature technology which uses microorganisms to decompose

organic waste and produce biogas. Many AD systems have been built in European countries and the

US for municipal, industrial, and agricultural waste treatment, and are recommended for COD

concentrations higher than 4,000 mg/L (Cuellar-Bermudez et al., 2017). AD is a straightforward

technology for microalgae biomass valorization and is preferred over biodiesel or bioethanol

production since it avoids the drying step of the biomass and the three macromolecules (namely

carbohydrates, proteins and lipids) are all converted to biogas (Molinuevo-Salces et al., 2016). The

integration of the AD process and microalgae cultivation as a means to improve discharge effluent

quality and methane yield has been investigated by the food industry. A variety of experimental

studies has investigated the use of swine manure as a substrate to achieve high algal growth and

then use the algal biomass as substrate for methane production. Molinuevo-Salces et al. (2016)

tested the efficiency of a microalgae consortium to treat swine slurry at different temperatures,

illumination periods and initial nitrogen concentrations (80 and 250 mg/L as ammonium). The swine

manure was filtered and diluted approximately 7 and 22 times to achieve the desired ammonium

concentrations of around 250 and 80 mg/L N-NH4, respectively. Three microalgae species, i.e.

Chlorella vulgaris, Scenedesmus obliquus and Chlamydomonas reindhardtii, were chosen based on

their robustness to grow in wastewater. Favorable culture conditions (23 oC and 14 h of illumination)

and high ammonium loads resulted in higher biomass production and greater nutrients removal

rates. Methane yields in the range of 106-146 and 171 ml CH4 g COD-1 were obtained for the

biomasses grown in batch and semi-continuous mode, respectively. Hernández et al. (2013) tested a

culture of Chlorella sorokiniana and aerobic bacteria on pig manure to produce second generation

biofuels. Temperature and illumination were at 24 oC and 6000 lux for 12 hours per day. AD results

showed that methane yield was highly influenced by substrate/inoculum ratio and by lipids

concentration of the biomass. A maximum methane yield of 518 ml CH4 g COD-1 was obtained.

Efforts on AD have been focused on the optimization of biogas yield and degradation of the volatile

solids; however, the management and post-treatment of the AD effluent has largely been overlooked

(Cai et al., 2013). AD effluents are typically low in carbon and high in ammonium nitrogen and

phosphorus. Most of the AD effluent is separated by a dewatering system into liquid and solid

fractions. The solid portion is usually composted then marketed as potting media or soil amendment,

while the liquid portion is traditionally used as fertilizer for land application (Cai et al., 2013). Due to

stringent regulations for discharge and the high nutrient concentrations typically found in AD

effluents, efficient and cost-effective nutrient recovery methods should be considered in order to

reduce the risk of nitrogen and phosphorus pollution from AD. The use of microalgae cultivation to

treat AD effluents has started to be considered as a cost-effective solution that can decrease the

nutrient content of the AD effluent thus meeting strict discharge criteria as well as enhance the

production of methane by recycling the growing algae biomass back to the AD. Dilution of AD

effluent is usually needed before feeding to microalgae cultivation systems in order to avoid the

potential inhibition of algal growth due to high ammonium concentration and turbidity (Cai et al.,

2013). In addition, as there is a significant amount of bacteria in AD effluent, proper pretreatments,

such as filtration and autoclave, may be necessary to prevent the contamination of algae production

systems (Cai et al., 2013).

Nutrient recovery from AD piggery effluent by microalgae has gained renewed interest over the last

decade (Nwoba et al., 2016, and reference therein). Among the microalgae species, Chlorella sp. and

Scenedesmus sp. appear to be the most robust and versatile due to tolerance to different

wastewater conditions (Nwoba et al., 2016). The R&D Centre at Murdoch University has a strong

capability in the application of microalgae cultivation systems to AD effluents. Ayre (2013)

successfully harvested Chlorella species in a mixed algae culture with Scenedesmus species and

diatoms. The mixed strain algal culture grew on undiluted and untreated AD piggery effluents

sourced from an Australian piggery. The operations of raceway ponds were monitored over a course

of 20 weeks with ammonia concentrations as high as 1,600 mg/L NH3-N. The work by Ayre (2013) has

shown that algal harvesting on piggery wastewaters is a promising application and the harvested

biomass can potentially be used either as food source to enhance pig production or as a biomass to

enrich the AD process. The author argues that, in order to sustain a quality controlled food source,

growth of a single strain of algae might be the most attractive option for obtaining consistent

protein, lipid and nutrient characteristics. Less control over the purity of the culture is required if

algal biomass is to be used to enhance the production of methane by AD. Alternatively, algal biomass

can also be used as a crop fertilizer. In all these scenarios the harvest of algae on AD effluents is seen

as a positive impact on the operation costs and environmental footprint of Australian piggeries.

Following the study by Ayre (2013), Nwoba et al. (2016) compared the growth of algae on piggery AD

effluents in two different configurations, i.e. a paddle wheel raceway pond and a closed

photobioreactor. Sand-filtered, undiluted AD piggery effluent was treated. While no significant

differences were detected between the cultivation systems, the overall carbohydrate, lipid and

protein contents of the consortium revealed its suitability to be used as animal feed or potential

biofuel feedstock. The consortium was maintained in semi-continuous culture for more than three

months without changes in the algal composition, thus indicating a promising outcome towards

further testing and piloting of the proposed process. A recent study by Wang et al. (2016)

demonstrated the successful growth of Chlorella vulgaris in a large scale application. Large-scale

application was conducted in an open raceway pond with undiluted anaerobically treated piggery

wastewater. The initial concentrations and removal rate of nitrogen and phosphorous were 421 mg/L

TN and 89.5%, and 60 mg/L TP and 85.3%, respectively.

9.2.3 Application of microalgae cultivation in the meat processing industry

The adverse effects on the environment of abattoir wastewaters call for new processes capable of

reducing the organic content and nutrient concentrations prior recycle and/or discharge of the

treated effluent. Anaerobic (e.g., AD) and aerobic (e.g., nitrification to denitrification through

activated sludge) treatments are commonly used in abattoirs; however, some major limitations exist.

Although anaerobic treatments efficiently remove organic matters whilst producing biogas, nutrient

removal is not effectively performed and high nitrogen and phosphorus concentrations are found in

the effluent. Aerobic treatments are well known for efficiently removing organic matter as well as

nutrients; however, their high energy requirement makes these methods expensive. Following the

advantages of algal cultivation systems and their widespread use for wastewater treatment,

researchers have recently started to investigate the integration of microalgae cultivation for the

treatment of abattoir wastewaters.

Maroneze et al. (2014) studied the performance of microalgal heterotrophic bioreactors in the

secondary treatment of cattle abattoir wastewater. The objective was to improve the effluent water

quality and produce algal biomass for biodiesel production. The authors tested the alternative

process of substituting conventional treatments (e.g., activated sludge and anaerobic systems) with

microalgae-based systems in the secondary treatment of the wastewater. The wastewater

composition was 7,692 ± 5193 mg/L COD, 155 ± 80 mg/L TKN and 23 ± 10 mg/L P-PO4. No

wastewater dilution was done before treatment by algae. Phormidium, which is a genus of single-cell

blue green algae that belongs to cyanobacteria phylum, was grown in this experiment. The

microalgal heterotrophic bioreactor converted in the order of 90% of COD, 57% of N-TKN, and 52% of

P-PO4 in algal biomass. The nitrogen removal in the heterotrophic microalgal bioreactor was

attributed to bioconversion of nitrogen into algal biomass as well as other non-biological processes,

such as air stripping, ammonia volatilization, absorption, and sedimentation. Phosphorus removal

was related to microalgal uptake, chemical precipitation and biosorption by microalgal biomass.

Taskan (2016) investigated organic matter and nutrient removal from abattoir wastewaters by a

mixed microalgae culture (i.e. eukaryotic and cyanobacterial species) grown in a closed photo-

bioreactor. The abattoir wastewater was filtrated with a microfiltration membrane to remove

particles after it was sterilized by autoclaving. The main characteristics of the raw wastewater were

197 mg/L TOC, 102 mg/L TN, 18 mg/L TP. Pure as well as diluted wastewaters were used as substrate

for algal cultivation. After 7 days of cultivation, the highest removal percentages of total organic

carbon, total nitrogen, and total phosphorus were 90%, 70% and 96%, respectively. The dilution ratio

was found to strongly impact on organic matter and nutrient removal performances. The highest

amount of TOC removal was obtained from the pure wastewater confirming the high carbon removal

capacity of mixed algal photo-bioreactors. TN removal was severely affected by its initial

concentration and gradually increased with the increase of TN concentration in the wastewater. The

highest nitrogen removal was achieved on undiluted wastewaters by biological assimilation. The

removal of phosphorous was not affected by its concentration in the initial feed and was higher than

93% for all dilution ratios. The algal growth results indicated that the abattoir wastewater was a good

source of nutrients and organic matter for the growth of algae. The high nutrient concentration of

undiluted wastewaters has been shown as a potential source for algal biomass production associated

with biodiesel production. The results indicated that cyanobacterial species were more efficient than

eukaryotic species in removing nutrients.

Hernandez et al. (2016) studied the performance of two high rate algal ponds treating pig abattoir

wastewaters. The objective was to produce biofuels (biodiesel, methane) from microalgae biomass.

The wastewater was diluted 3 times using tap water to feed the ponds. The main characteristics of

raw wastewater were 1,621 ± 81 mg/L COD, 9.2 ± 0.5 mg/L NH4-N, 1.4 ± 0.1 mg/L TP. One pond was

placed indoors under controlled conditions of temperature and light supply, while the other pond

was placed in a greenhouse. The microalgae consortium was composed by Chlamydomonas

subcaudata, Anabaena sp. and Nitzschia sp. High removal efficiencies were achieved in the high rate

algal pond placed indoor (92%, 80% and 71%) and placed in the greenhouse (86%, 79% and 91%) for

COD, ammonium and phosphorous, respectively. The authors identified that, despite the high

biochemical methane potential, productivity is often low as a result of the strong microalgal cell walls

that hinder the bacterial attack. A pre-treatment of microalgal biomass is therefore suggested as a

way to enhance its biodegradability and increase methane production.

A summary of relevant publications on microalgae cultivation systems used in the wastewater

treatment by the food and meat processing industry is given in Tables A2.1 and A2.2.

Disclaimer:

The information contained within this publication has been prepared by a third party commissioned by Australian Meat Processor Corporation Ltd

(AMPC). It does not necessarily reflect the opinion or position of AMPC. Care is taken to ensure the accuracy of the information contained in this publication. However, AMPC cannot accept responsibility for the accuracy or completeness of the information or opinions contained in this publication, nor does it endorse or adopt the information contained in this report.

No part of this work may be reproduced, copied, published, communicated or adapted in any form or by any means (electronic or otherwise) without the express written permission of Australian Meat Processor Corporation Ltd. All rights are expressly reserved. Requests for further authorisation should be directed to the Executive Chairman, AMPC, Suite 1, Level 5, 110 Walker Street North Sydney NSW.

Table A2.1. Selected literature on the application of microalgae cultivation systems for the treatment of wastewaters generated by the food and processing industry. Primarily treated wastewaters are used as substrate for algal growth.

Reference Wastewater source Microalgae species Wastewater characterisation as feed to

microalgae (mg/L) Performance (% removal)

COD TN TP COD TN TP

Fallowfield and Garrett (1985)

Piggery raw wastewater – primarily treated and 9 times diluted

Chlorella

137.2 18.8 98 as BOD 54 - 98 42 - 89

Zhu et al. (2013)

Piggery raw wastewater – primarily treated and diluted

Chlorella zofingiensis 3,500 ± 63

(pre-dilution)

148 ± 4 (pre-dilution)

156 ± 8 (pre-

dilution) 66 - 80 69 - 83 85 - 100

Maroneze et al. (2014)

Beef abattoir wastewater – primarily treated and no dilution

Phormidium species 7,692 ± 5,193

155 ± 80 as TKN

23 ± 10 as PO4

90 57 52

Hernandez et al. (2016)

Pig abattoir wastewater – primarily treated and 3 times dilution

Chlamydomonas subcaudata, Anabaena species and Nitzschia species

1,621 ± 81 (pre-

dilution)

149 ± 12 as TKN (pre-dilution)

1.4 ± 0.2 (pre-

dilution) 86-92

79-80 (as NH4)

71-91 (as PO4)

Molinuevo-Salces et al. (2016)

Swine manure – filtered and 7 to 22 times diluted

Chlorella vulgaris, Scenedesmus obliquus and Chlamydomonas reindhardtii

3,750 ± 64 (pre-

dilution)

1,762 ± 41 (pre-

dilution) 80 – 250 (post-dilution) as

NH4

161 ± 2 (pre-

dilution)

96-99 (as NH4)

82 - 100

Taskan (2016) Beef abattoir wastewater – primarily treated by sterilisation and filtration (no dilution)

Eukaryotic and cyanobacterial species

197 as TOC 102 18 90 70 96

Table A2.2. Selected literature on the application of microalgae cultivation systems for the treatment of wastewaters generated by the food and processing industry. Secondarily treated wastewaters are used as substrate for algal growth.

Reference Wastewater source Microalgae species Wastewater characterisation as feed to

microalgae (mg/L) Performance (% removal)

COD TN TP COD TN TP

Abou-Shanab et al. (2013)

Piggery wastewater effluents – biologically treated by anaerobic/oxic process

Chlamydomonas Mexicana

571 ± 8 as total carbon

56 ± 2 13 ± 0.6

29 62 28

Ayre (2013) Piggery wastewater effluents – post AD, no dilution

220 (as TOC) 690 - 1,600 as

NH4 43

Hernández et al. (2013)

Pig manure – primarily and biologically treated by nitrification denitrification

Chlorella sorokiniana and aerobic bacteria

616 ± 45 218 ± 20 50 ± 9 62 83 for NH4

58

Wang et al. (2016)

Piggery wastewater effluents – post AD, no dilution

Chlorella vulgaris 745 ± 7 290 ± 3 24 ± 2 42 - 73 89 85

Disclaimer:

The information contained within this publication has been prepared by a third party commissioned by Australian Meat Processor Corporation Ltd

(AMPC). It does not necessarily reflect the opinion or position of AMPC. Care is taken to ensure the accuracy of the information contained in this publication. However, AMPC cannot accept responsibility for the accuracy or completeness of the information or opinions contained in this publication, nor does it endorse or adopt the information contained in this report.

No part of this work may be reproduced, copied, published, communicated or adapted in any form or by any means (electronic or otherwise) without the express written permission of Australian Meat Processor Corporation Ltd. All rights are expressly reserved. Requests for further authorisation should be directed to the Executive Chairman, AMPC, Suite 1, Level 5, 110 Walker Street North Sydney NSW.

9.3 Appendix 3. Alternative water sources for integration with microalgae

cultivation

9.3.1 Site G abattoir

Two streams have been identified at Site G that could be potentially integrated with the microalgae

cultivation process.

The effluent of the anaerobic pond (Stream 4, Figure A3.1) is a good candidate for microalgae

harvesting due to its low concentration of FOG and BOD and high nutrient content (Table A1.8). The

concentration range of nitrogen and phosphorus is within the literature values (151 ± 42 mg/L and 26

± 7 mg/L for TN and TP respectively) and the relatively low variability over time (low standard

deviation) guarantees a consistent load of nutrients into the microalgae cultivation system.

Moreover, given the low efficiency of removal of nitrogen by the existing aerobic treatment (Tables

A1.12 and A1.13), the microalgae cultivation process could substitute the aerobic treatments

currently used at Site G and improve the effluent water quality in terms of both nitrogen and

phosphorus concentration and load. The reconfiguration of the wastewater streams is proposed in

Figure A3.1.

The effluent of primary treatments (saveall and settling pond) could also be a good candidate for

microalgae harvesting (Stream 3, Figure A3.2). The concentration of nutrients is similar to the post

AD measurements and within the range of literature values suitable for microalgae growth. The

concentration of BOD in Stream 3 is measured at 664 ± 1,040 mg/L (Table A1.8). By considering a

BOD to COD ratio of 0.5 (Bazrafshan et al., 2012; Sunder and Satyanarayan, 2013) and the upper

range of the BOD variability (large standard deviation of 1,040 mg/L), the concentration of COD in

Stream 3 can be estimated in a range of 1,328 - 2,080 mg/L. Although this COD concentration might

be too high for microalgae to grow, it is still within the range tested by Maroneze et al. (2014) and

Hernandez et al. (2016). The concentration of FOG (179 ± 219 mg/L) could, however, limit the growth

of microalgae on Stream 3 due to the growth of competitive bacteria. The reconfiguration of the

wastewater streams is proposed in Figure A3.2. Experimental tests are recommended to verify the

suitability of Stream 3 as a substrate for microalgae growth. If successful, the microalgae process

could substitute the full biological treatment process of anaerobic and aerobic treatments.

Although a comprehensive long term dataset on water quality has been provided by Site G,

wastewater flowrates are not available at the moment due to an outdated monitoring system. An

estimate of wastewater flowrate of 1,750 kL/d has been used in this report to calculate the mass and

energy balances of the proposed microalgae cultivation system (refer to Appendix 9.1 for details on

how the wastewater flow rate was estimated).

Figure A3.1. Flowsheet of the wastewater treatment plant at Site G which includes the proposed microalgae cultivation process (highlighted in red) applied on the AD effluent (Stream 4).

Figure A3.2. Flowsheet of the wastewater treatment plant at Site G which includes the proposed microalgae cultivation process (highlighted in red) applied on the primarily treated wastewater

effluent (Stream 3).

9.3.2 Site A, C and D abattoirs

AD effluent characterization

Sites A, C and D follow a conventional treatment of their wastewaters which include screening and

solid separation, dissolved air flotation units for fat and oil separation, and then combination of the

wastewater streams in mixed tanks/open pits before entering anaerobic ponds/lagoons. Data on

Sites A, C and D are sourced from the MLA/AMPC reports written by Jensen and Batstone (2012,

2013); however the AD effluent characterization was not given in those reports. Personal

communication with one of the authors of the reviewed reports provided the composition of the AD

effluent for Sites A and D. The nutrient concentration in the AD effluent at Site D is also reported in

the MLA/AMPC report by Jensen (2015). AD effluent data are not available for Site C. The pre and

post AD data at Sites A, C and D are summarized in Table A3.1.

An estimate of the AD effluent is calculated for Site C, as well as for the post AD FOG concentration

at the three sites. Literature data on the efficiencies of removal of COD, BOD, FOG and nutrients by

covered anaerobic lagoons are used as reference as these systems are currently operating at the

selected Australian abattoirs. Mittal (2006) describes a typical low-rate anaerobic system (e.g.,

anaerobic lagoons and ponds) as a 3 to 5 m deep pond with a retention time of 5 to 10 days. Typical

reductions of up to 97% BOD, 95% SS and 96% COD are reported in the literature (Mittal, 2006, and

reference therein). In his MLA/AMPC report, Laginestra (2012) reviewed the efficiencies of covered

anaerobic lagoons at a variety of Australian abattoirs. Despite a large variation in pond volume and

hydraulic retention time, the COD removal varies from 80 to 88%, the BOD removal from 63 to 80%

and the FOG removal from 83 to 95% (Laginestra, 2012). Typical effluent quality from anaerobic

lagoons ranges from 500 to 1,500 mg/L BOD, depending on inflow and system optimization

(Laginestra, 2012). No indication on nutrient removal is given in the report. COD removal efficiencies

at Site A and D are calculated at 95% and 91%, respectively (Table A3.1), thus in line with literature

values (Mittal, 2006). Based on literature data and removal efficiencies calculated at Sites A and D, a

COD removal efficiency of 90% is assumed for Site C and a post AD COD concentration of 1,079 mg/L

is estimated (Table A3.1, italics highlighted value). FOG removal by AD is considered equal to the

average value given by Laginestra (2012) and equal to 89%. Post AD FOG concentrations are

estimated for Sites A, C and D (Table A3.1).

The organic component of TKN and TKP normally accumulates in the AD pond (e.g., 40 to 50%

accumulation of total phosphorous has been reported in anaerobic lagoons, Jensen, 2015); however,

phosphorus as soluble PO4 and nitrogen as NH4 are found in the post AD effluent at high

concentrations due to their release during anaerobic digestion processes. Removal of total nitrogen

as low as 35% by AD is reported in the literature (Mittal, 2006). At Sites A and D, pre AD TKN is mostly

formed by organic bound nitrogen and only a relatively small fraction is present as ammonia nitrogen

(NH4/TKN of 24% and 9% at Sites A and D, respectively, Table A3.1). On the contrary, post AD TKN is

almost totally formed by ammonia-nitrogen as a consequence of its release during the biological

degradation process (NH4/TKN of 98% and 90% at Sites A and D, respectively, Table A3.1). As of

phosphorous, at Site D, pre AD TKP is almost equally partitioned between organic bound phosphorus

and phosphate, whilst post AD phosphorous is mostly formed by phosphate (Table A3.1). Mainly

phosphate is measured at Site A both pre and post AD (Table A3.1). Overall, a large fraction of

organic bound nitrogen and organic bound phosphorous accumulates in the anaerobic lagoon at

Sites A and D, whilst high concentrations of ammonia and phosphate are found in post AD streams.

The release of ammonia during the microbial digestion process at Sites A and D caused a 4 and 6

times increase of the post AD ammonia concentration, respectively (Table A3.1). Based on the post

AD ammonia increase measured at Sites A and C, we assume a 5 times increase (average value

between 4 and 6 as found at Sites A and D) in the concentration of ammonia post AD occurs at Site C.

The concentration of ammonia in the post AD effluent at Site C is therefore estimated at 310 mg/L

(Table A3.1). Due to the scarcity of data regarding phosphorus removal, we assumed that organic

bound phosphorous at Site C is expected to accumulate in the AD process, whilst the same pre and

post AD phosphate concentration is found at Site C (Table A3.1).

A reliable characterization of the post AD effluent is fundamental for a meaningful mass and energy

balances of the microalgae cultivation system. Due to the uncertainty of our assumptions and the

absence of measured nutrient values on the AD effluent at Site C, major focus is given on Sites A and

D, for which a more reliable dataset is available.

Table A3.1. Wastewater characterization pre and post AD at Sites A, C and D. Data are taken from Jensen and Batstone 2012, Jensen and Batstone 2013, Jensen 2015. NA: not available data. Italics

highlighted values are estimated based on literature and measured data.

Site A Site C Site D

Combined wastewater Pre AD Post AD Pre AD Post AD Pre AD Post AD

Volume (kL/d) 2,423 NA 2,115 NA 2,150 NA

TCOD (mg/L) 12,893 700 10,785 1,079 12,460 1,100

TS (mg/L) 8,396 NA 7,530 NA 7,401 NA

FOG (mg/L) 2,332 257 3,350 369 1,240 136

TKN (mg/L) 245 245 260 NA 438 254

NH4-N (mg/L) 58 239 62 310 38 229

TKP (mg/L) 58 38 30 NA 56 34

PO4-P (mg/L) 53 33 15 15 27 32

Selected wastewater streams

Although the nitrogen and phosphorous concentrations measured at Sites A and D are within the

range measured at Site G and literature values, the concentrations of FOG and COD measured in the

combined wastewater prior to AD are very high, thus making the pre AD stream not suitable for

integration with a microalgae harvesting process (Tables A1.1 and A1.4).

Amongst the wastewater streams generated within the slaughtering process (Tables A1.1 and A1.4,

Site A and D, respectively), some of them are characterized by a low organic and high nutrient

content, thus making them suitable to be treated by microalgae. In particular:

• At Site A, the wastewater streams generated from cattle wash (SP 1, Table A1.1) and from the

kill floor (SP 4, Table A1.1) could be combined and sent to a microalgae cultivation system. The

composition of the resulting combined stream is reported in Table A3.2. The calculated COD

concentration is 3,384 mg/L which is within the range of COD tested by Maroneze et al. (2014)

and Hernandez et al. (2016). Following the integration with a microalgae cultivation process, the

proposed reconfiguration of the process flowsheet is shown in Figure A3.3. Following the

adoption of a microalgae cultivation system, the composition of Stream SP 8 would change and

be the same as Stream SP 2 (Table A1.1). A proper mass balance is calculated in the next section

to determine the final wastewater composition entering the microalgae cultivation system.

• At Site D, the wastewater streams generated from cattle wash (SP 22, Table A1.4) and from the

kill floor (SP 9, Table A1.4) could be used as substrate for microalgae harvesting. The

composition of the resulting combined stream is reported in Table A3.2. The concentration of

FOG might be too high (213 mg/L) for microalgae growth. If this is the case, Stream SP 9

generated by washing down the kill floor needs to be excluded from the microalgae treatment.

The proposed reconfiguration of the process flowsheet is shown in Figure A3.4. A proper mass

balance is calculated in the next section to determine the final wastewater composition entering

the microalgae cultivation system.

Table A3.2. Characterization of the proposed combined streams for the integration with the microalgae cultivation process at Sites A and D.

Abattoir Stream Volume (kL/d)

TCOD (mg/L)

TS (mg/L)

FOG (mg/L)

TKN (mg/L)

NH4-N (mg/L)

TKP (mg/L)

PO4-P (mg/L)

Site A Combined streams SP 1 + SP 4

1,332 3,384 3,169 72 742 37 18 10

Site D Combined streams SP 9 + SP 22

1,122 2,064 2,398 213 145 34 19 5

Figure A3.3. Reconfiguration of the process flowsheet at Site A. Black dotted lines: current flowsheet. Red lines: proposed reconfiguration by directing streams SP1 and SP4 to microalgae

cultivation. SP: sample point.

Figure A3.4. Reconfiguration of the process flowsheet at Site D. Black dotted lines: current flowsheet. Red lines: proposed reconfiguration by directing streams SP9 and SP22 to microalgae

cultivation. SP: sample point.

Mass balance on selected wastewater streams

Although the AD effluent is considered the most suitable stream to grow microalgae on due to the

low concentration of organics (COD and FOG) and high concentrations of ammonia and phosphorus,

alternative wastewater streams generated by washing of cattle and kill floor have been identified at

Sites A and D as potentially suitable for integration with the microalgae cultivation process. The

composition of kill floor and cattle wash streams show a relatively low concentration of COD and

FOG, as well as an adequate concentration of ammonia and phosphorus to grow algae (Table A1.1

and A1.4). The integration of kill floor and cattle wash wastewaters within the microalgae cultivation

process considerably impacts on the process currently in place at Sites A and D, and requires a

reconfiguration of the current flowsheet. By considering Site D as an example, the integration of kill

floor (stream number SP9) and cattle wash (stream number SP22) wastewaters within the microalgae

cultivation process causes changes in the current flowsheet as shown in Figure A3.4. Stream SP9 will

by-pass preliminary treatments and both SP9 and SP22 will by-pass AD to be directly sent to

microalgae cultivation (red lines, Figure A3.4). Such a reconfiguration of the process flowsheet will

inevitably impact on the quantity and quality of the wastewater entering AD, therefore a mass

balance on the impacted streams needs to be calculated.

The quantity and quality of each process stream refer to Table A1.4. Daily mass fluxes are calculated

based on the volume of each stream (in kL/d) and each component concentration. Daily fluxes are

reported in Table A3.3. The removal of SP9 from its current process streamline will affect the

composition of SP7, SP3, and SP2. Similarly, the removal of SP22 will affect the composition of SP2.

The composition of the affected streams (SP7, SP3, SP2, and AD effluent, as well as SP9, SP22,

combined stream to microalgae) is summarized in Table A3.4. Note that the efficiency of removal of

COD, FOG and nutrients by preliminary treatments (i.e., rotating drum and saveall) and by the AD

have been calculated based on the removal rates as per mass balance (Table A3.3). Following the

reconfiguration as proposed in Figure A3.4, the composition of the wastewater entering the AD

process changes significantly. By comparing the composition of SP2 in Table A3.4 with its original

composition in Table A1.4, it should be noted that i) the volume of water entering AD has halved

(from 2,150 to 1,078 kL/d), ii) the concentration of COD increased from 12,460 mg/L to 21,267 mg/L,

and iii) both TKN and TKP increased significantly. These changes are a consequence of the fact that a

significant volume of wastewater (about 1,100 kL/d, sum of SP9 and SP22) with lower COD

concentrations has been removed from the mix of streams entering AD, thus leading to a more

concentrated pre AD stream. The post AD stream as calculated in Table A3.4 has COD and FOG

concentrations that are potentially suitable to be treated in a microalgae cultivation system; however

the ammonia and phosphate concentrations are almost double the post AD stream in the original

case (compare AD effluent streams in Table A1.4 and Table A3.4).

It has to be noted that the COD concentration in the three streams (AD effluent, kill floor + cattle

wash, combined post AD + kill floor + cattle wash) is about 1,900 mg/L (Table A3.4). Such a

concentration of COD might be too high for a pure microalgae system as bacteria contamination

could occur due to the high concentration of organics. This aspect will need to be assessed by specific

bioprospecting experimental studies where a particular consortium of microalgae that is able to grow

on the selected streams is identified.

The reconfiguration of the wastewater streams as proposed in Figure A3.4 and Table A3.4 has a

considerable impact on the existing AD process due to the lower volume and higher strength of the

new stream entering AD. The proposed solution does not seem to be optimal for the existing Site D

abattoir and the integration of the microalgae cultivation system on the AD effluent only is

considered a more practical solution for Site D. These calculations, however, suggest that, whether a

new wastewater treatment plant is to be designed and a microalgae system considered, it is

recommended to look at alternative streams within the slaughtering process to be integrated with

the microalgae cultivation system. Both options of blending all streams together or design a

dedicated microalgae cultivation system for each selected stream should be assessed during

feasibility studies.

Similar results are obtained on Site A (Tables A3.5 and A3.6).

Table A3.3. Daily mass fluxes of each component in the wastewater streams at Site D. SP: sample point (refer to process flowsheet, Figure A3.4).

ID Stream Volume (kL/d)

TCOD (kg/d)

TS (kg/d)

FOG (kg/d)

TKN (kg/d)

NH4-N (kg/d)

TKP (kg/d)

PO4-P (kg/d)

SP25 Paunch - pre screen 200 2,438 3,025 28 53 4 33 20

SP4 Paunch - post screen 200 1,084 1,389 39 49 3 29 18

SP24 Paunch - solids 18 2,649 4,489 20 14 NA 4 NA

SP21 Cattle wash - pre auger 400 4,428 3,931 33 142 34 26 12

SP22 Cattle wash - post auger

400 720 792 4 52 35 7 4

SP23 Cattle wash - solids 2 179 312 1 4 NA 1 NA

SP10 Combined bins 304 13,419 9,287 2,826 631 55 50 27

SP11 Combined stick 94 6,901 3,152 1,981 46 20 11 3

SP12 Veal room 480 6,778 4,481 2 141 12 2 7

SP9 Kill floor/offal 722 1,596 1,899 235 111 4 14 2

SP7 Combined red - pre screen

1,600 15,920 13,582 6,002 565 61 62 26

SP6 SaveAll in 1,600 20,464 14,822 5,280 672 43 66 30

SP3 SaveAll out 1,600 12,832 6,450 1,565 643 61 66 53

SP2 Combined wastewater prior to AD

2,150 26,789 15,912 2,666 942 82 120 58

Post AD effluent 2,150 2,365 NA 292 546 492 73 69

Table A3.4. Calculated composition of wastewater streams affected by the reconfiguration of the process flowsheet after integration with microalgae cultivation system. Site D. SP: sample point

(refer to process flowsheet, Figure A3.4).

Volume (kL/d)

TCOD (mg/L)

TS (mg/L)

FOG (mg/L)

TKN (mg/L)

NH4-N (mg/L)

TKP (mg/L)

PO4-P (mg/L)

SP7 Combined red - pre screen

878 30,863 19,270 5,478 932 100 71 43

SP3 SaveAll out 878 24,876 9,150 1,428 932 100 71 43

SP2 Combined wastewater prior to AD

1,078 21,267 8,741 1,199 804 83 85 51

Post AD effluent 1,078 1,877 NA 132 466 503 52 61

SP9 + SP22 Kill floor + cattle wash 1,122 2,064 2,398 213 145 34 19 5

post AD effluent + SP9 + SP22

Combined stream to microalgae

2,200 1,973 NA 173 303 264 35 32

Table A3.5. Daily mass fluxes of each component in the wastewater streams at Site A. SP: sample point (refer to process flowsheet, Figure A3.3).

ID Stream Volume (kL/d)

TCOD (kg/d)

TS (kg/d)

FOG (kg/d)

TKN (kg/d)

NH4-N (kg/d)

TKP (kg/d)

PO4-P (kg/d)

SP 1 Cattle wash 882 2,817 2,646 4 78 41 11 5

SP 2 Paunch liquid 311 7,435 4,914 810 161 11 66 50

SP 3 Paunch, tripe, green wash

330 10,793 8,184 1,281 93 5 51 33

SP 4 Kill floor 450 1,690 1,575 93 909 8 13 8

SP 5 Tripe wash 54 1,668 1,075 628 15 0 4 2

SP 7 New Render 192 7,681 4,723 1,063 330 8 23 14

SP 8 Primary treated wastewater cold

1,512 26,909 17,416 5,033 384 110 127 123

SP 9 Primary treated wastewater hot

911 6,567 4,373 1,037 241 40 26 15

Combined wastewater prior to AD

2,423 32,929 21,443 5,956 626 148 148 135

Table A3.6. Calculated composition of wastewater streams affected by the reconfiguration of the process flowsheet as proposed after integration with microalgae cultivation system. Site A. SP:

sample point (refer to process flowsheet, Figure A3.3).

Volume (kL/d)

TCOD (mg/L)

TS (mg/L)

FOG (mg/L)

TKN (mg/L)

NH4-N (mg/L)

TKP (mg/L)

PO4-P (mg/L)

Combined wastewater prior to AD

1,222 11,459 7,600 1,511 328 42 75 53

Post AD effluent 1,222 622 NA 167 328 173 49 33

SP1 + SP4

Kill floor + cattle wash 1,332 3,384 3,169 72 742 37 18 10

post AD effluent + SP1 + SP4

Combined streams to microalgae

2,554 2,062 NA 117 544 102 33 21

9.4 Appendix 4. Environmental impact and risk assessment

9.4.1 Guidelines for recycling of wastewater effluents in abattoirs

During this project, quantitative water quality guidelines applicable to the recycle of treated

wastewater effluents at local as well as Australia-wide scale abattoirs have been referred to. Table

A4.1 summarizes the water quality guidelines that are applicable to the permitted on-site and off-site

uses of treated wastewaters in abattoirs. The main source of this information is the AGWR (Tables

3.8 and 4.10, AGWR, 2006), the AQIS meat notice (AQIS, 2008) and some information given by Site G

personnel on local limits Site G abattoir must comply with. Although there has been a common

perception that any water reuse and recycling would be unacceptable to export meat

establishments, it is also expected and recommended by AQIS that the Australian meat processing

industry would decrease its water usage by an efficient recycle of the treated wastewater effluent

(AQIS, 2008). AQIS is in ongoing contact with regulatory agencies in Australia’s export meat markets

regarding the use of recycled and reuse water in abattoirs, and has incorporated their positions into

the draft meat notice (AQIS, 2008; Warnecke et al., 2008). Table A4.1 focuses on those on-site and

off-site uses where the wastewater has to be treated to fit-for-purpose levels without necessarily

achieving potable quality. It should be noted that the list of AQIS-approved processes where the use

of recycled wastewater is permitted is expected to grow, following successful validation and

implementation by abattoirs (Warnecke et al., 2008). In abattoir wastewaters, the main potential

hazards are caused by pathogens, pharmaceutical, nutrients and ammonia concentrations (Table 2.3,

AGWR, 2006). The following analysis will mostly focus on nitrogen and phosphorous content.

9.4.2 Conventional treatment process at Sites A, D and G

Sites A, D and G follow a conventional treatment of their wastewaters which include screening and

solid separation, dissolved air flotation for fat, oil and grease separation, and then combination of

the wastewater streams in mixed tanks before entering anaerobic ponds/lagoons. Methane is

collected during the AD process at Sites A and D and used as an energy source within the abattoir

operations to lower their carbon footprint. No methane collection occurs at Site G. The composition

of the AD effluents at Sites A, D and G is reported in Table A4.2. The management and post-

treatment of the AD effluents generated in abattoirs have largely been overlooked, despite their

major environmental impacts due to the high volumes of nutrient-rich wastewaters produced on a

daily basis (Cai et al., 2013). The high nutrient content prevents the discharge of AD effluents into

surface water bodies (compare nutrient concentrations in Table A4.2 with guidelines in Table A4.1).

The quality of the AD effluents generated in abattoirs would allow the discharge of AD effluents into

sewer systems for further treatment in off-site wastewater treatment plants; however, the costs

associated with conveyance and off-site treatment make this option unfeasible. Typically, the

management of AD effluents generated in abattoirs involves the storage of high volumes of water in

evaporation ponds. After some retention time in the ponds (normally > 25 days as per AGWR, 2006),

part of the water is used for irrigation of fields and paddocks. The advantages of storage ponds is

that they are cheap, robust and easy to maintain, they provide a buffer to dilute possible peaks in

chemical and microbial hazards as well as reduce enteric pathogens (AGWR, 2006). The reduction of

nutrient concentration is however very low and high evaporation rates cause an increase in nitrogen,

phosphorous and salinity in the long term. Moreover, volatilization of nitrogen into ammonia gas can

occur, thus increasing the carbon footprint of the abattoir due to potential emission of greenhouse

gases.

Table A4.1. Water quality standards applicable to the recycle of treated wastewater effluent for

on-site and off-site non-potable uses.

Permitted uses of recycled wastewater Water quality target Source

On-site • Secondary treatment + disinfection

and/or lagoon detention (> 25 days)

• BOD < 20 mg/L

• SS < 30 mg/L

• E. Coli < 100 cfu/100mL

• TN < 40 mg/L 1

• NH4-N < 35 mg/L 1

• TP < 12 mg/L 1

AGWR, 2006

Cleaning of yards, infrastructures and trucks

Washing of animals (other than final wash)

Animal drinking water (older than 12 months)

Fire control

Steam production

Toilet flushing

Irrigation of green areas

Off-site

Irrigation of crops for fodder production

• Secondary treatment + disinfection and/or lagoon detention (> 25 days)

• BOD < 20 mg/L

• SS < 30 mg/L

• E. Coli < 100 cfu/100mL

• TN < 40 mg/L 1

• NH4-N < 35 mg/L 1

• TP < 12 mg/L 1

• BOD < 50 mg/L 2

• BOD < 30 kg/year/hectare 2

• TDS < 1,500 mg/L 2

• TN < 300 kg/year 2

• TP < 50 kg/year 2

AGWR, 2006 Site G abattoir

Final discharge

To sewer

• BOD: 300 – 3,000 mg/L

• COD: 900 – 9,000 mg/L

• TSS: 1,000 – 1,500 mg/L

• TN: not specified

• FOG: 50 - 200 mg/L

AGWR, 2006

To surface water

• BOD: 5 – 10 mg/L

• COD: 15 – 30 mg/L

• TSS: 10 – 15 mg/L

• TN: 0.1 – 15 mg/L

• FOG: 2 - 15 mg/L

AGWR, 2006

1 Indicative value given in Table 4.10 by the AGWR (2006). Values are not site-specific and might not be applicable to the abattoirs discussed in this project. 2 Refer to Site G only.

Table A4.2. Composition of the treated wastewater effluents at Sites A, D and G. NA: not available data. Italics highlighted values are estimated based on literature data and assumptions made by

the authors.

Volume (kL/d)

TCOD (mg/L)

TS (mg/L)

FOG (mg/L)

TKN (mg/L)

NH4-N (mg/L)

TKP (mg/L)

PO4-P (mg/L)

Site A – AD effluent 2,423 700 NA 257 245 239 38 33

Site D – AD effluent 2,150 1,100 NA 136 254 229 34 32

Site G – AD effluent 1,750 54 ± 54 as BOD

530 ± 770 as TSS

8 ± 5 151 ± 42 as

TN NA

26 ± 7 as TP

NA

Site G – storage pond effluent

45 12 ± 12 as BOD

70 ± 64 as TSS

7 ± 5 78 ± 30 as

TN NA

24 ± 5 as TP

NA

Site G – annual load from storage pond effluent used for irrigation

173

kg/year as BOD

501 kg/year as TSS

777

kg/year as TN

245

kg/year as TP

The use of treated abattoir wastewater for irrigation is widely applied in abattoirs as it represents a

low-cost approach of wastewater management and can act as a good source of nutrients for infertile

soil (Matheyarasu et al., 2015). The impacts of the discharge of abattoir wastewaters into the

environment (soil, air and water) through crop irrigation are broadly classified into health and social

impacts, and ecological impacts. As for health and social impacts, possible pathogens contamination

of the surface and groundwater sources and odor spread during irrigation of sites constitute the

most relevant impacts associated with the use of abattoir wastewaters for irrigation. The ecological

impacts related to the storage in open ponds of wastewater effluents and their use for crop irrigation

include:

• Generation of large volumes of water with high nutrient concentrations, thus not suitable for

on-site recycle, except for irrigation of gardens, green areas and trees;

• Possible greenhouse gas emissions due to storage in open ponds of large volumes of water with

elevated content of ammonia nitrogen;

• Potential eutrophication of soils and surface waters, nutrient imbalance, pest and disease in

plants due to the high content of nitrogen and phosphorous in the water used for irrigation

(toxicity of phosphorous to some native plants, AGWR, 2006);

• Potential nitrogen contamination to groundwater;

• Inefficient use of large areas of land dedicated to evaporation and storage ponds;

• Potential uncontrolled growth of algae (e.g., algal blooms) with spread of potentially toxic algal

species;

• Loss of the environmental and economic value of the treated wastewater effluent associated

with potential resource recovery of water, nitrogen and phosphorus.

Due to the detrimental environmental impacts associated with the use of abattoir wastewaters for

irrigation, it is crucial that the following steps are considered (Matheyarasu et al., 2015):

• The discharged wastewater should not exceed the acceptable level of nutrients and pollutants,

both in terms of concentration and loading rates;

• Microbial community should be eradicated through disinfection;

• The environmental standards (legislation/law) defined by the state environmental authority

should be strictly followed;

• Pollution levels are to be reduced through various treatment techniques to retain the environ‐

mental quality.

The concentration of the treated wastewaters after retention in storage ponds is not available for

Sites A and D; however, data are available for Site G (Table A4.2). Based on the guidelines

summarized in Table A4.1, the concentration of nutrients in the final effluent at Site G is too high for

recycle in uses other than irrigation of gardens, green areas and trees. As a consequence, only a small

portion of the water stored in the storage ponds (on average 45 kL/d, Table A4.2) is reused for

irrigation, thus leaving the majority of the water in ponds. Even when used for irrigation, the annual

loads at Site G often exceed the local limits on the nutrient loading rates (compare Table A4.1 and

Table A4.2).

The environmental impact and risk assessment of the conventional treatment system, management

and uses of the wastewater effluents currently implemented at Sites A, D and G is summarized in

Table A4.4. Nitrogen and phosphorous are considered the main environmental hazards. Based on the

hazards and current uses of the treated wastewater, general environmental endpoints identified for

consideration are groundwater, surface water, and soil. Air might also be impacted by the possible

volatilization of untreated ammonia in the AD effluents while stored in evaporation ponds. Based on

the current uses and the guidelines on the nitrogen and phosphorous concentrations, the high

nutrient content in the wastewater effluent at Sites A, D and G identify potential high risks to the

environment, thus requiring preventive measures to reduce the risk. More thorough and further

treatments of the AD effluents are considered the most, and only, effective measure to lower the risk

of high nutrient contamination. The objective of further treatment is mainly to ensure nutrients level

in the wastewater effluents comply with the guidelines given in the AGWR (2006) in order to allow

recycling and reuse of the treated wastewater. Once the environmental impacts and associated risks

are managed from moderate/high to low/acceptable, the residual risks related to the identified uses

are minimized and the environmental impacts reduced to acceptable levels.

A series of alternative treatments of AD effluents aiming at reducing nitrogen concentrations have

been reviewed in a MLA/AMPC report by Jensen et al. (2013). The suggested solutions involve

technologies such as nitrification/denitrification by activated sludge, anaerobic ammonium removal

by ANNAMOX, and constructed wetlands (Jensen et al., 2013). Each technology presents several

limitations that have hindered their adoption on a large scale. Activated sludge has elevated energy

demand, thus high costs associated with aeration. Anaerobic ammonium removal processes are

limited by high COD to ammonium ratios and by large fractions of non-degradable COD, both

characteristics typically found in AD effluents from abattoirs wastewaters (Jensen et al., 2013).

Constructed wetlands are easy to operate; however, they have shown poor nutrient removal rates

and prohibitively large footprint (the wastewater production expected from Australian

slaughterhouses is in the range of 1,000-3,000 kL/d which could require a wetland trench length in

the range of 50-100 km, Jensen et al., 2013). The study by Jensen et al. (2013) concludes that an

optimal treatment process has not been uniquely defined yet and has to be determined on a case by

case basis. Microalgae cultivation systems might find a competitive niche application in the

treatment of AD effluents from abattoirs.

9.4.3 Microalgae cultivation system at Sites D and G

Based on the mass balance developed in Section 5.4, the integration of the microalgae cultivation

system on the AD effluent at Sites D and G generates two product streams: a concentrated

microalgae biomass product and a wastewater effluent stream that is depleted in nutrients. The

estimated composition of each product stream at each abattoir is summarized in Table A4.3. A full

characterization of the quality of the treated wastewater effluent post microalgae cultivation is not

available at this stage, as only through pilot testing the exact determination of the final stream

composition can be quantified.

Table A4.3. Composition of the treated wastewater effluents at Sites D and G when the microalgae

cultivation system is integrated with the current treatment process flowsheet. NA: not available

data.

Volume (kL/d)

Algae biomass (g/L)

Algae biomass (kg/d)

NH4-N (mg/L)

PO4-P (mg/L)

Site D

Algal biomass stream 17 300 5,221 NA NA

Wastewater effluent 1,270 0.05 64 0 < 0. 5

Site G

Algal biomass stream 9 300 2,802 NA NA

Wastewater effluent 1,300 0.05 64 0 as TN 1.4 as TP

The environmental impact and risk assessment is summarized in Table A4.4. A qualitative

characterization of the environmental risks is determined by following the procedure described in

Chapter 4 and Table 2.7 of the AGWR (2006). The concentration and loads of nitrogen, phosphorous

and the residual concentration of algae biomass in the wastewater effluent are considered the main

potential hazards. The residual concentration of algae biomass potentially present in the wastewater

effluent is due to the assumed 90% efficiency of the dewatering and harvesting system. The presence

of algae biomass represents a potential hazard related to the reuse and recycle of the wastewater

effluent; however, specific guidelines are not well defined in the AQIS Meat Notice (AQIS, 2008) or in

the Australian Guidelines for Water Recycling (AGWR, 2006). A detailed evaluation of the potential

toxicity associated with the presence of algae biomass in the wastewater effluent is required and

further filtration before reuse of the wastewater effluent might be necessary.

A nutrient-depleted wastewater effluent of about 1,300 kL/d at Sites D and G is a high-value process

output. Subjected to water recycling guidelines implemented at each abattoir, the nutrient-depleted

wastewater effluent can be recycled within the abattoir operations for all the uses proposed in Table

A4.4. Treated wastewater recycling improves the environmental footprint of each abattoir by

reducing quantity and costs associated with freshwater usage. If recycle is not viable, the nutrient-

depleted wastewater effluent is likely to meet the guidelines for safe discharge into surface waters

(Table A4.1). The environmental endpoints potentially impacted by the recycling of the wastewater

effluent are soil, surface water, groundwater and the abattoir’s wastewater treatment plant. Off-

sites uses, such as discharge to surface water bodies and irrigation of pasture for fodder production,

are expected to cause environmental impacts such as nutrient imbalance, eutrophication and

contamination. However, due to the low nutrient content in the wastewater effluent treated by the

AD-microalgae cultivation process, the risk associated with such environmental impacts is classified

as ‘low’, thus no preventive measures are required. On-site uses of the wastewater effluent can

potentially cause contamination of potable water if the reticulation system is not well designed,

operated and maintained, thus raising the potential risks to ‘high’ (Table A4.4). Preventative

measures that guarantee a complete separation of potable and recycling water distribution systems

are required, together with proper personnel training and Hazard Analysis Critical Control Point

(HACCP) procedures (Table A4.4). Whenever these preventative measures do not lower the risk to

acceptable levels, a stricter regulation on the permitted on-site uses of recycled wastewater is

required until the risk is classified as ‘low’.

The final use of the concentrated microalgae biomass has to be evaluated on a case-by-case basis

depending on the location and needs of the abattoir, local market for algae products, costs of

handling and transportation of the biomass. Amongst its possible uses, on-site uses such as biogas

production through recycle to AD, use as fertilizer for crop irrigation, and use as animal feed are

some technically feasible and cost effective uses of the algae product (Table A4.4). Off-site uses such

as pharmaceutical products and biofuel generation could also be possible depending on the local

market and the grown algal strain (Table A4.4). The evaluation of the environmental impacts

associated with off-site uses of the algae biomass requires a full life cycle assessment, which at this

stage is considered of low benefit to the current high-level desktop study due to the scarcity of data

on each abattoir and process uncertainty (bioprospecting experimental tests are needed to lower the

process uncertainty). The environmental impacts associated with the on-site uses of the biomass are

not associated with potential risks as they are expected to improve the environmental footprint of

the abattoir. The use of microalgae biomass (in particular Chlorella species) as crops fertilizer has

shown to lead to positive effects on the environment in terms of the health of soils and plants.

Similarly, the use of microalgae as animal feed has shown great potential in recent studies

(Benemann, 2013), with Chlorella being one of the most robust and versatile species in the market.

In summary, positive and negative environmental impacts have been found for the integrated AD-

microalgae cultivation process. The main negative environmental impact is associated with the

recycle of the wastewater effluent for on-site operations such as cleaning of yards, infrastructures

and trucks, washing of animals, and animal drinking water. Possible contamination of the potable

water mains due to poor maintenance, design and/or misuse of the recycled water reticulation can

lead to high risks of contamination of meat products, thus making preventive measures and

appropriate hazard managing procedures a priority to minimise the risks. Another negative

environmental impact relates to the large land footprint dedicated to microalgae cultivation systems

in open ponds (21 and 11 hectares have been calculated for Sites D and G, respectively).

Several positive environmental impacts of the microalgae cultivation process have been identified as

follows:

• Reclamation of the environmental and economic value contained in the wastewater effluent in

terms of water and nutrient recovery;

• Generation of large volumes of water that are suitable for recycling for on-site and off-site uses

or safe to discharge to surface water bodies;

• Generation of an algae biomass product that is suitable for re-use within the abattoir’s

operations or for sale to available markets.

• Sequestration of carbon dioxide currently generated by abattoirs during the current wastewater

treatment process and fixation into algae biomass.

A comparison between the conventional treatment process and the integrated microalgae cultivation

system points out that, under conventional treatments, large volumes of wastewaters are mostly

stored in open ponds. This practice leads to potentially high environmental risks as identified in the

environmental impact assessment. The wastewater effluents often do not adhere to the guidelines

for water recycling and significantly impact soil, surface water, groundwater and air. Moreover,

conventional treatments currently adopted in abattoirs do not consider the intrinsic value of water

and nutrients within the wastewater effluent, thus wasting resources potentially suitable for

recovery. From an environmental perspective, further treatment of the wastewater effluent is

therefore unavoidable.

The microalgae cultivation system mitigates, and possibly removes, the environmental impacts

associated with contamination of soils, water and groundwater, and to greenhouse gas emissions

into the air. More importantly, it gives value to the wastewater effluent by recovering the nutrients

and water and ultimately improving the environmental footprint of the abattoir. The main source of

negative environmental impacts of the integrated microalgae cultivation process is related to

possible misuse of the recycled water within the abattoir operations in those operations where

recycled water use is not permitted. However, proper preventative measures can reduce the risk to

acceptable level. In the scenario where recycled wastewater effluent is too risky to be used on-site,

off-site uses and/or discharge to surface water bodies are not representing an environmental hazard

due to the quality of wastewater complying within the applicable guidelines.

Table A4.4. Comparison of the environmental impact and risk assessment at Sites D and G between the current conventional wastewater treatment and the proposed integrated microalgae

cultivation process.

Conventional treatment Integrated microalgae cultivation system

Wastewater treatment process

• Primary treatments - screening and solid separation - dissolved air flotation for fat, oil and grease

separation

• Secondary treatments - anaerobic digestion (AD) in covered lagoon for

COD and FOG removal - aerobic pond for nitrogen removal (Site G only)

• Storage/evaporation ponds

• Possible filtration of wastewater effluent before recycling

• Primary treatments - screening and solid separation - dissolved air flotation for fat, oil and grease

separation

• Secondary treatments - anaerobic digestion (AD) in covered lagoon

for COD and FOG removal with biogas recovery

- microalgae cultivation system on AD effluent for nitrogen and phosphorous recovery in algal biomass

• Possible filtration of wastewater effluent before recycling

Hazards

• Nitrogen

• Phosphorous

• Nitrogen

• Phosphorous

• Algae biomass in wastewater effluent

Management and use of treated wastewater effluent

• Storage in evaporation ponds

• Irrigation of crops and pasture for fodder production

Uses of wastewater effluent

• On-site uses (i.e., cleaning of yards, infrastructures and trucks, washing of animals other than final wash, animal drinking water, fire control, irrigation of gardens and green areas)

• Off-site irrigation of crops and pasture for fodder production

• Off-site discharge to surface water bodies Uses of algae biomass

• On-site recycle to AD lagoon to improve biogas generation

• On-site use as fertiliser on crops

• On-site use as animal feed

• Off-site use as pharmaceutical products

• Off-site use as biofuel generation

Environmental endpoints

• Soil

• Surface water

• Groundwater

• Air

• Soil

• Surface water

• Groundwater

• Wastewater treatment plant for on-site uses

Adverse environmental Impacts

• Nutrient imbalance in soil causing toxicity and disease to plants and soils

• Nitrogen contamination of groundwater

• Eutrophication of surface water bodies due to nitrogen and phosphorous

• Emission of greenhouse gases

• On-site contamination of potable water distribution system

• Large land footprint

• Large land footprint

Qualitative risk estimation

• The concentration of nutrients in the treated wastewater effluents at Sites D and G (Table A4.2) exceed the AGWR guidelines (Table A4.1)

• The likelihood of the identified environmental impacts relative to the uses of the treated wastewaters is considered ‘likely’

• The consequences of the identified environmental impacts can vary from ‘insignificant’ to ‘moderate’

• The risk associated with the management of the treated wastewater is classified as varying from low to high

• Preventative measures are required

• The concentrations of nutrients in the wastewater effluent at Sites D and G (Table A4.2) comply with the AGWR guidelines (Table A4.1)

• The wastewater effluent is not treated to potable standards

• The consequences of on-site contamination of the potable water distribution system due to the recycle of non-potable wastewater effluent can vary from ‘minor’ to ‘major’

• The likelihood of on-site contamination of the potable water distribution system due to the recycle of non-potable wastewater effluent is considered ‘possible’

• The risk associated with on-site uses of wastewater effluent is high

• Preventative measures are required

Preventative Measures

• On-site treatment technologies aiming at reducing the nutrient content in the final effluent

• Removal of nitrogen and phosphorous through specific technologies (chemical precipitation and nitrogen biological removal)

• Recovery of nutrients in a usable form (e.g., fertiliser)

• Reticulation distributing recycled wastewater effluent needs to be separated from potable water distribution systems

• Personnel training and proper Hazard Analysis Critical Control Point (HACCP) procedures need to be put in place as defined by the Australian Standards AS4696 2007 (Browne, 2007) to manage accidents and minimise risks

• Avoid the reuse of the wastewater effluent in situation where contamination with potable water reticulation might happen

Qualitative residual risk estimation

• The concentration of nutrients in the treated wastewater effluents at Sites D and G is expected to comply with the AGWR guidelines (Table A4.1)

• The likelihood of the identified environmental impacts relative to the uses of treated wastewaters is expected to change from ‘likely’ to ‘unlikely’

• The consequences of the identified environmental impacts can vary from ‘insignificant’ to ‘minor’

• The residual risk is expected to be low

• The likelihood of on-site contamination of the potable water distribution system from the use of non-potable wastewater effluent is considered ‘rare’

• The consequences of on-site contamination of the potable water distribution system due to the recycle of non-potable wastewater effluent can vary from ‘minor’ to ‘moderate’

• The residual risk is determined as low

9.4.4 Review of LCA studies on microalgae cultivation

Life cycle assessment (LCA) studies are designed to consider all environmental impacts of a process,

from ‘‘cradle to grave’’ (i.e., considers the sources of all inputs and fate of all products and wastes).

LCAs are related to net energy analyses and are a very common tool used to assess the sustainability

of a process. In his review of LCA studies on microalgae cultivation for biofuel production (Benemann

et al., 2012), the worldwide renown algae expert John Benemann points out how most of the

published studies are based on assumptions derived from experimental outcomes and theoretical

knowledge of the process rather than from existing production systems, thus making the conclusions

of the LCAs rather limited and problematic. The author suggests the need of LCA and techno-

economic analyses to be developed together and in an iterative way, in order to envision and

implement a feasible process that must operate within the constraints of existing practical and

theoretical knowledge. This process will then set the objectives of R&D projects for pilot testing.

In their effort to reliably compare LCA studies and present the range of process possibilities and

potential environmental impacts, Handler et al. (2012) presented a detailed examination of

microalgae LCAs with a particular focus on the growth stage of algae in raceway ponds. Literature

data and environmental impact factors were synthesized to focus on three main indicators, i.e.,

greenhouse gas (GHG) emissions, energy demand, and fresh water use for each literature source, all

normalized to a consistent functional unit (1 kg of cultivated algae). In all cases, the environmental

impacts of algae cultivation across all impact categories were highly variable, covering a range of

over two orders of magnitude:

• GHG emissions per kg of cultivated algae range from 0.1 to 4.4 kg CO2eq., with the main

contributors including electricity inputs for gas compression and movement, and pond water

movement;

• Energy requirements per kg of cultivated algae vary by almost two orders of magnitude (0.154 –

14.59 MJ), most studies ranging between 0.6 and 2 MJ, with an average of 1.7 MJ;

• Makeup water to replenish for evaporation and leakage losses also varies widely between 1.3

and 105 L per kg of cultivated algae.

Recent sustainability studies have shown that the indirect energy input associated with nutrients

supply constitutes a major energy cost and environmental burden during microalgae cultivation

(Alcantara et al., 2013). However, the integration of microalgae cultivation systems with high

nutrient wastewater effluents like abattoir AD effluents can significantly improve those

environmental impacts associated with energy inputs for nutrient supply. Sander and Murthy (2010)

performed an LCA study on a microalgae cultivation experiment for biodiesel production. Secondarily

treated wastewater is used as a substrate for microalgae growth and it is assumed all nutrients

needed for algae to grow are supplied from the wastewater (i.e., a similar scenario to the integrated

microalgae process in abattoirs). The experiment is based on a 4 day harvest–growth–harvest cycle.

The functional unit is 1,000 MJ of energy from algal biodiesel (24 kg of algal biodiesel). The authors

quantified energy demand and CO2 emission for the growth step in raceway ponds as equal to 15.43

MJ/functional unit and 0 kg/functional unit, respectively. The harvest and dewatering steps have a

larger impact on energy demand and CO2 emission (3,000 – 6,000 MJ for energy demand and 240 –

400 kg CO2 emitted) depending on the used technology for algae concentration (filter press versus

centrifuge). Through a LCA study on microalgae cultivation in raceway ponds, Clarens et al. (2010)

demonstrated the advantages of using wastewater effluents as a substrate for algae growth. Average

concentrations of total nitrogen and phosphorous equal to 25 and 7 mg/L, respectively, were

measured in the growing medium. Although the nutrient content of the wastewaters used by Clarens

et al. (2010) are not comparable with the wastewater effluents generated at Sites A, D and G, the

study quantifies the improved environmental impacts from using wastewaters as a substrate for

algae growth (Table A4.5). Substantial reductions in GHG emissions, energy and water use of the

microalgae cultivation stage are found when wastewaters are used as a growth substrate (Table 6).

Table A4.5. Results of LCA on microalgae growth on a freshwater and wastewater substrate

derived by Clarens et al. (2010). Results are expressed per functional unit (317 GJ biomass-derived

energy) and refer to the cultivation stage in open raceway ponds.

Freshwater

Wastewater (TN = 25 mg/L; TP = 7 mg/L)

GHG emission (kg CO2eq.)

Mean ± standard deviation 1.8 ± 0.59 1.1 ± 0.56

Percentage reduction relative to freshwater LCA (%) 39

Energy demand (MJ)

Mean ± standard deviation 30 ± 6.6 2.4 ± 6.2

Percentage reduction relative to freshwater LCA (%) 92

Water use (m3 x 104)

Mean ± standard deviation 12 ± 2.4 9.4 ± 2.2

Percentage reduction relative to freshwater LCA (%) 22

Of particular interest for abattoir wastewater treatment plants equipped with a post AD nutrient

removal stage (like Site G, for example), Clarens et al. (2010) found that the extremely energy-

intensive nature of nutrient removal processes is likely to generate a higher energy burden than

microalgae cultivation. About 60-80% of energy consumption during wastewater treatment is

associated with nutrient removal, and wastewaters with higher nutrient concentrations are more

environmentally burdensome to treat. Clarens et al. (2010) suggests that rerouting a portion of the

nutrient load to algae cultivation is one way to reduce energy consumption during wastewater

treatment, and also note that reductions in each life cycle impact category associated with avoidance

of nutrient removal in wastewater treatment plants account for 50-70% of the total offsets. The

conclusions of this study are quite relevant to abattoirs like Site G (where a nutrient removal process

is currently adopted) as it shows how the environmental impacts (e.g., energy use, GHG emission and

water use) of the wastewater treatment process could be minimized by integrating a microalgae

cultivation step within the current system. A full LCA study on Site G abattoir is highly recommended

once more data and an experimental study on algae bioprospecting and growth on the AD effluent

are available. It is expected that the integrated microalgae process proposed in this project would

significantly improve the environmental impacts of the operations at Site G abattoir.

The reviewed LCA studies are not directly inter-comparable because of different functional units

defined in each study; however, they quantify the environmental impacts of microalgae cultivation

and suggest the use of high nutrient wastewater effluents as a growth substrate to minimize the

environmental impacts associated with GHG emission, energy use and water demand. In the context

of abattoir operations and wastewater treatment, whether the microalgae cultivation system is

grown on fresh or waste water, its environmental impacts in terms of GHG emission, energy demand

and water use are expected to be significantly lower than the environmental impacts generated from

abattoirs operations. The environmental performance review on Australian abattoirs published by

AMPC (Ridoutt et al., 2015) quantified the GHG emission, energy demand and water use of abattoirs

per unit product (tonnes of HSCW) as an average of 432 kg CO2eq., 3,000 MJ and 8,000 L,

respectively. The impacts on the environment of the cultivation of microalgae to treat the

wastewater generated in abattoirs thus constitute a small fraction of the overall environmental

impacts of the abattoirs.

9.4.5 Final use of the algae biomass and its environmental impact

Environmental impact assessments, techno-economic analyses and LCAs of microalgae cultivation

systems are strongly related to the final use of the algae biomass. During the course of this project, a

variety of off-site and on-site uses of the algae biomass product has been mentioned, e.g., biodiesel

production, pharmaceutical products and oil extraction, animal feed, fertilizer and biogas production

through recycle of algae biomass to AD. The most cost effective utilization of the algae biomass

needs to be evaluated for each abattoir separately as it depends on the abattoir location, local

market for algae products, process and techno-economic site assessment and conditions. It should

be noted that the primary objective of integrating a microalgae cultivation step in the wastewater

treatment process implemented at abattoirs is to reduce the environmental impacts associated with

high nitrogen and phosphorus concentrations in the treated wastewater effluents currently

generated in abattoirs. Thus the production of a nutrient-depleted water stream that can be recycled

within the abattoir operations and/or safely discharge to the environment is the main end-product of

the treatment process. In this context, the ability of microalgae cultivation systems to achieve high

nutrient removal rates and generate a clean water stream is well understood in both the literature

and practical applications. The production of clean water is then considered an achievable outcome

and positive environmental impact of the process, due to the maturity of algae cultivation systems.

In turn, negative environmental impacts are related to the energy demand, and subsequent GHG

emissions, of the algae cultivation, harvesting and dewatering systems. In the context of wastewater

treatment in abattoirs (where the most important end-product is a clean water stream), the grown

algae biomass represents a process by-product whose inherent value can be exploited as a way to

reduce and minimize the energy demand of the system. The perspective of our study substantially

differs from the one found in the majority of LCA and environmental impact assessment studies

where the main target is the conversion of algae biomass to biofuels. In the abattoir context, the final

use of the biomass must therefore be related towards an environmentally sustainable and/or cost-

effective solution. Uses of algae biomass for biofuel production are expected not to be competitive in

the abattoir context due to specific process requirements that increase the energy demand of the

cultivation and dewatering steps (e.g., high algae daily productivity and high biomass concentrations

as percentage solids required for transportation and oil extraction). Technologies developed to

produce bio-oil, e.g., such as hydrothermal liquefaction, that do not require dry algae biomass are

not considered mature enough as fuel yields, quality and costs are yet to be determined (Benemann,

2013). Microalgae biomass revalorization through AD has been suggested as a promising process that

involves AD on the raw algae biomass to produce methane as biofuel (Alcantara et al, 2013;

Hernandez et al., 2016; Molinuevo-Salces et al., 2016; Polakovicova et al., 2012; Zhang et al., 2016).

Because this process by-passes the algae concentration and oil extraction steps, both responsible for

about 50% of production costs (Collet et al., 2011), it represents an attractive option for the biofuel

industry. Digestion of pure algae biomass or co-digestion of algae and bacteria are both well studied

in the literature as possible ways to maximize the methane yield (Wang and Park, 2015; Yuan et al.,

2012; Alcantara et al., 2013). The production of electricity from biogas generated in the AD of algae

biomass is expected to offset the energy demand of the cultivation, harvesting and dewatering steps,

thus significantly improving the environmental impacts of entire system. Although attractive from

the energy perspective, the re-valorization of algae biomass through AD in not compatible with

abattoir wastewater systems as nitrogen and phosphorous are re-dissolved in the AD liquid digestate

and a high nutrient stream is generated. Collet et al. (2011) and Ras et al. (2011) have determined

the remineralization percentage of nutrients as varying with the hydraulic retention time (HRT) of the

AD process, which highlights a trade-off between nutrient mineralization and methane production

during AD of microalgae Chlorella vulgaris. An HRT of 16 days caused 19% of the nitrogen content in

biomass to mineralize and a methane conversion rate of 147 mL CH4/g VSS (Ras et al., 2011). An HRT

of 28 days caused 68% of the nitrogen content in the algae biomass to dissolve, although the

methane conversion rate increased to 240 mL CH4/g VSS (Ras et al., 2011). A 90% nitrogen

mineralization and a methane conversion of 292 mL CH4/g VSS was suggested by Collet et al. (2011)

at an HRT of 46 days.

Collet et al. (2011) undertook a LCA and environmental assessment of the use of methane from algae

as a biofuel. The system is composed of raceway ponds, a dewatering system by settling and

centrifugation with the concentrated algae biomass sent to an AD reactor for biogas production. The

water from the algae concentration step and the liquid digestate from AD are recycled back to the

ponds to make up for evaporation and water losses. A fraction of the biogas (about 26%) is recycled

within the AD process as heat, with the rest of the biogas being purified to methane and used to

produce electricity. CO2 is provided to the algae ponds from external sources and nutrients from

added fertilizers are recovered from the recycle liquid digestate. Collet et al. (2011) estimated the

total electric consumption equal at 0.64 kWh/kg of algae (3.2 kWh/m3 of methane and 16,000

kWh/d) for the whole system and the most consuming stages as:

• the paddlewheels: 31.2%

• the pumping between the ponds and the settlers: 23.9%

• the anaerobic digestion plant: 20.8%, with 16.9% for the mixing of the digesters and the

pumping, and 3.9% for the centrifugation of the digestates

• the purification plant: 13%

• the centrifugation of the algae: 6.6%

• the CO2 injection: 4.5%

Although attractive for its ability to generate electricity and offset the energy demand of the algae

cultivation, harvesting and dewatering process, the AD of the whole biomass produced daily is

impractical in the selected abattoirs due to the remineralization of nitrogen and phosphorous. The

use of biomass as fertilizer and animal feed is possibly the most appropriate option at the selected

abattoirs. These uses will translate in potential revenue and/or economic savings for the abattoirs

operations, and possibly offset the cost associated with the energy demand of the cultivation and

dewatering system. The use of algae biomass as protein supplement in animal feed has been widely

suggested and researched as a sustainable way to help address the global energy, food and

environmental crisis and the current competition for resources (e.g., land and water) between animal

feed and human food supply (Benemann, 2013; Lum et al., 2013; Bleakley and Hayes, 2017). Recent

estimates indicate that 30% of the global algal production is used by the animal feed industry and,

although their nutritional profiles vary considerably with the species used, a large majority is

characterized by protein, carbohydrate, and lipid contents that are comparable, if not superior, to

conventional feeds (Lum et al., 2013). Lum et al. (2013) reviewed several applications of using

sewage-grown Chlorella and Scenedesmus (both algae that have been demonstrated to grow well on

high nutrient wastewaters; Nwoba et al., 2016, and Ayre et al., 2017) to supplement the diet of

chickens due to their high crude protein and carotenoid contents. In order to make it more digestible

for use as animal feed, the harvested biomass has to go through cell breakage to extract the protein

content (Benemann, 2013). A process that has been recently suggested in the literature is the

integration of biogas production and animal feed through microalgae: the protein content of the

algae biomass can be extracted and used as animal feed, whilst the remaining fraction that is high in

carbon and lipids can be anaerobically digested to produce methane (Lum et al., 2013; Benemann,

2013). By this process, the use of microalgae biomass in animal feed is expected to not only improve

human and animal food security, but also facilitate cost-effective biogas production and reduces

greenhouse gas production (Lum et al., 2013, and references therein). Such process could be an

attractive option for abattoirs as it would avoid the remineralization of nitrogen and phosphorus

during the AD of algae biomass while producing electricity from biogas.